The "Deaths Head" skull was the equivalent of a battle flag for Jaster Mereel's regiment. So, yeah, they are basically the only ones that can get away with wearing it.

My only guess is that since Jaster Mereel's fleet was the last army standing, Durge is either masking himself as a former warrior or something along the lines of mocking the Mandalorians for fun, to spite them.

Boba wears it in tribute to Papa Fett most likely. I have also drawn the conclusion that the Mandalorian Wheat logo w/ the letter F and the blood drop is in memorium of Fett's parents, who were farmers, slain by a rogue group of Mandalorians. Althought said group was never given a designation, it was more than likely the "Death Watch".

Jango Fett's Expanded Universe story has been tons of fun to get into, and is definately better than most anything I have ever bothered looking into.

and all of the black/blue Batmobile in at least 1 TRU.