American Sign Language,
gang signs and the hand signals
used by commando teams
are all gesture languages.

It is very hard to fake or interpret
an unfamiliar gesture language.

A deaf person doesn't know
Crips from Bloods
and even seemingly transparent gestures
like a smile
might be rude or worse
in a culture where showing one's teeth
is thought to be
a sign of aggression.

Sometimes its good to have rules.
No language which contains
only 13 gestures
could be complete.

Note that there is no gesture for

DANGER:
YOU ARE ABOUT TO
KNOCK OVER A TELEPHONE POLE!