Tiny to fit uniform insignia on 28mm figures, or just small to fit 28mm banners and vehicles?
If small for vehicles/banners/etc is what you want, Company B has these, one white and one black sheet:
They're midway down the
Company B decal page - Ctrl+F for "skull" is probably the fastest way to find them there.
Otherwise, maybe freehand?
(both off my own blog,
SPAD here and
armoured car here.)
For the freehand, I used a few light pencil marks as initial guides, then just took it slowly with the brush. I had to paint back into the shape a couple of places to tidy things up after the white went on, mind you.