Make an initials mark
Type the letters, pick a hand, and get a transparent PNG cut to the strokes.
How it works
A contract that asks for initials is asking for something different from the signature at the end. The signature closes the document. The initials are an acknowledgement attached to one page or one clause: a mark that the page was there and was read when the whole was agreed. Solicitors ask for them because a stack of loose sheets can have a page swapped after the fact, and a per-page mark makes the substitution visible. Handwritten amendments are initialled for the same reason. Adobe Acrobat's Fill and Sign keeps an initials mark as a separate saved item from the signature, and forms routinely ask for both.
Two letters is a different problem from twenty
Tracking is applied per gap, and two capitals share one gap where ten letters share nine. A value that opens a full name up by a visible amount is nearly invisible across a pair, because it is spent once instead of nine times. Script capitals make the difference sharper: they carry entry and exit flourishes that reach sideways past the advance width, so the gap the metrics describe and the gap the eye reads are two different numbers. The render here measures every glyph's ink box rather than its advance, for exactly that reason, and sizes the canvas from the ink.
A full stop between the letters is a spacing device as much as a punctuation mark. It takes an advance width of its own and sits on the baseline, so the same pair of capitals is wider with the stops than without them at identical tracking, and it reads more slowly: the eye crosses two stopping points rather than one gap. Which form a person uses is house style, and neither is more correct. The separated setting draws what is typed, stops and case included. The joined and monogram settings remove full stops and spaces, and the line under the result counts what was removed.
Weight, and reading as the same hand
Outlines scale linearly, so a face set at twice the em draws strokes twice as thick. An initials mark and a signature cut from the same face rarely land at the same em: the signature spends its width on a dozen glyphs or more, the initials spend theirs on two or three, so the initials are set larger to fill a box of comparable height. On the same page the heavier strokes read as a different pen, and to a careful reader as a different hand. Stroke weight here works in finished pixels, and thinning an initials mark by one or two is usually the correction.
Separated, joined, or a monogram
Separated is the plain form and the safe default. Joined pulls the letters together into a single unit, which suits a box too small to hold anything spaced out. Monogram draws a middle letter larger, the traditional arrangement in which the surname initial sits in the centre at greater size with the given names flanking it. A middle letter exists only when the count is odd, so two or four letters are drawn at one size and the result line says so rather than picking a letter to emphasise.
Sized for a box measured in millimetres
Size is set as a height, not a width. The constraint on a form is the height of the box, and two marks of equal width containing two letters and four letters have letters of quite different sizes. Three hundred pixels is one inch at 300 dots per inch, or 25.4 mm. An initials box 15 mm across works out at 177 pixels at the same resolution, so there is little to gain above 600: the surplus pixels are thrown away by whatever places the image.
The PNG is trimmed to the ink bounding box before it is written, and the finished pixel dimensions are reported with the result. The reason is placement. An image carrying transparent padding is centred on the padding rather than on the mark, so dropping it into a 15 mm box leaves it sitting off to one side, and the error differs for every set of letters because the padding depends on which letters they are. Cut to the strokes, the centre of the file is the centre of the mark.
Questions
How many letters can I use?
Two or three is the ordinary case and one works fine. Four are drawn at the same quality, since the height is fixed and the width grows to hold them rather than the letters being squeezed. Above twelve characters the tool refuses and points at the signature generator, because a run that long is a name being set in a box built for a mark.
Will these match the signature I made on this site?
They will if you pick the same face and the same ink. Both pages offer Dancing Script, Great Vibes and Caveat, and both use the same three ink values, so the pair is consistent by construction. What will not match automatically is stroke weight, since the two marks are set at different em sizes. Thinning the initials by a pixel or two brings them into line.
What exactly does the joined setting change about what I typed?
It removes full stops, spaces and middle dots, then closes the remaining letters up by six per cent of the em before any adjustment you add. Nothing else is altered: case is left as typed, and no letter is substituted or reordered. The count of removed characters appears in the line under the result, so the change is never silent.
Can I drop this onto a PDF here?
Not as a file. The PDF signer on this site takes its mark from its own pad rather than from an uploaded image, so no handoff is offered from this page and none is implied. In Word or Google Docs, insert the PNG and set its wrapping to behind text. Preview on macOS and most PDF readers accept a pasted image directly on the page.
Why is the image not a square?
Because it is cut to the ink, and initials are wider than they are tall in every style here. A square would mean transparent padding on two sides, which is the thing that makes a dropped image sit off-centre in the box. Set the height you need and let the width follow the letters.