Bell squark/ strobe flash on set is ok according to NSI as it is just a momentary indication. There was a time when this was interpreted as not acceptable, but then apparently NSI said it was ok.
All about interpretation.
You can tell the outside world that you have set the alarm with a bell chirp or strobe on set, but it has to be momentary. Strange though that keypads have to shut down so as to not show armed state, according to NSI, but it's acceptable to tell everybody around the area with a bell chirp/ strobe flash that you have just armed ( or not, more to the point) the alarm system.
As with most things in our industry, not thought through.