[jarfil]

If binary has taught me anything, is that you can count up to 1024 with 10 fingers...

[masklinn]

If you've got flexible hands and independent-enough fingers you can even count in ternary, up to 59048 (though binary can also take advantage of toes for a limit of 1048573)

[Anarch157a]

Using your hands to signal 4 in binary could put you in a lot of trouble.