Where and when has this happened, other than in people's imagination? Do you have a cite?--snipped-- The last thing we want is for armed teachers to be running around with "Shoot Me!" hats, badges, jackets, or other devices recognizable to a mass shooter.
Note that every instance reported over the years has proven false, not truthful as reported.
Therefore IMHO, it has been confirmed repeatedly that OCing a handgun does not make one a primary target for the bad guy. So why would anyone logically think that these things would contribute any differently? Military and law enforcement excepted.
Bottom line though is let them carry in some manner.