Here are a couple of simple ASCII guns that you could send in a text message:
,_____, /_/' .'====' /_/'
You can find more than 4 dozen fancy guns done in ASCII text here.
The origins of ASCII art date all the way back to the mid 1960s, and are often attributed to Ken Knowlton who was working for Bell Labs at the time. It wasn't until the 1970s and 80s though, that ASCII art became more widespread through the use of BBS (Bulletin Board Systems) of the time, an early precursor to today's forums on web sites.