typeface samples showing the design of uppercase and lowercase Greek numerals Stigma and Koppa in various modern computer fonts. Notice how some G-shaped versions of capital Stigma in some fonts are indistinguishable from similar versions of Koppa in others (red)
Font designs:

MgOldTime UC Pol: by Magenta
Galatia SIL: by SIL International
Free Serif: by GNU FreeFont
Linux Libertine: by Libertine Open Fonts Project
Cardo: by David J. PerryOld Standard, Theano Didot: by Alexey Kryukov
SBL Greek: by Society of Biblical Literature
Alfios, Anaktoria: by George DourosIFAO-Grec: by Institut Français d'archéologie orientale
Palatino Linotopy: by Linotype
TITUS Cyberbit: by Bitstream Inc.
Aisa Unicode: by Stefan HagelNew Athena Unicode: American Philological Association
Vusillus: by Ralph Hancock
CMU Serif: by Andrey Panov
Own work
Future Perfect at Sunrise