The help text needs clarification.
This identifier is designed to be used with, for example, external user input in commands that may evaluate text later on, such as /timer commands. It delays evaluation of text for one level of evaluation.
This explanation leads one to believe it's used for delayed evaluation, not preventing a remote mSL injection.
BTW... on my system, using /timer 1 1 echo -a $unsafe(1 $chr(124) /echo 2) from the input line results in the following...
* Timer 1 activated
* Timer 1 halted
I'll look into it's probably something local... but certainly odd.