Kudos to Freewill, who offered this bit of insight into the BLAM! discovered in the bTV Halo footage at Marathon's Story yesterday:

I was fortunate enough to be looking over Joe's shoulder (with his permission of course!) when he was playing with the latest Halo build. The word BLAM seems to be 'fill-in' for the name of the weapon you are using. At one point Joe pressed a key that filled the left side of his screen with several translucent weapon 'slots', all saying BLAM and each highlighting as he switched between several weapons.

Interesting... one wonders if there will be a limited number of those slots to be filled. And while BLAM! is a good start, let's hope Bungie also keeps with their tradition of distinctive weapon names, and that Halo has a SPNKR of its own.