Well you may as well scrap your MM signals since that's just an old urban myth and if you think about it for a minute, it makes absolutely no sense whatsoever.
First, there is no need for them to send signals on Level 2, or L3 or the tape. Until Pink Sheets came out with their Pink Link (PLINK) platform all BB and Pink trading was done on the telephone, still is for BB's that are dually quoted on the Pinks. So why send silly signals when they can just tell each via phone, or instant message or now....with PLINK which allow them to message each other electronically.
Second, MM's employ thousands of traders. You think each new rookie trader they shove onto a few little stocks is given an MM signals code book? Gee, but every time someone quit, wouldn't they have to change all the codes.
Third...watch a Nasdaq stock like say MSFT trade sometime, wow all those 100, 200, 300 etc trades flying by every few seconds, man that's a lot of signals.
Best, and funniest thing the last few years, was when bonedaddy started making 911 trades all the time...now lots of people do it from time to time just to see the reactions of people that don't know any better.