I need help identifying Bushmaster markings on upper receivers. What should I be looking for?

To my knowlege, there are no Bushmaster markings per se on Bushie uppers, or anybody elses  (except Colt) for that matter. What's on the uppers are forge marks, and most all the aftermarket makers are using the same three or four forges.

Your best chance of IDing a Bushie upper is that it's not a Colt, and it is coated on the inside surfaces with a dry lube.  To my knowledge, only Colt and Bushie are coating their uppers w/the dry lube at the factory. Even if you find a dry lubed nonColt, tho, it still might be another brand that the owner sprayed w/the lube formula.

Colt does not use the dry lube only Bushmaster.  Also other manufacturers mark their uppers.  Armailte does for instance.

Colt still uses the Dry Film coating on their M4 uppers. Military Spec calls for a Dry Film coating on the inside of the upper.

Maybe they don't put it on their current Post Ban Match Target's...

Does Breakfree CLP dissolve dry lube?

It will eventually, after many cleanings.

If you use a harsh cleaner, like bore solvent, then that will take it right off.

I just bought a Colt M4 marked C AF flat top upper in the past few months.  It had no dry lube.  I am not aware of any milspec for the dry lube even in M4s.  Could you direct me to a link to that info?  Thanks.

Also according to Bushmaster the dry lube is there only for break in and will come off in just a few cleanings with CLP.  It is only there to assist with break in while parts are tight.