If it doesn't have a name on it, and it's in the parts area, or another area set aside for "up for grabs", it's up for grabs.
If it's elsewhere, and it's NOT labeled "up for grabs", it's NOT up for grabs.
This is one of the reasons the shop rules really need to get posted. Here's the snippet from that document on the wiki:
5. If its not explicitly labeled as free, or fair game, its not. (Still, please label your project materials.)
and here's another that's relevant to the condition of the classroom:
Clean up your own mess promptly. (And any mess you notice that's not in progress)
The classroom needs to get and stay clean; it's not happening, and people need to be trained. Now.
The other part of this is, I don't want to see, for example, the computer that Adam set up for the maker bot, get "up for grabbed" as it wasn't labeled.
We need to be clean, and we need to err on the side of not trashing someone's stuff.