I found an object in my yard.

[JDubb]

I think they're traps. They block out individual channels on a cable run. I've seen these in nursing homes where the Comcast service comes in and they block a channel with these so they can put their own community channel in place of what they're blocking.

Can I put it in between my tv and the cable hook up, and see what happens?

Yeah you should be able to. The worst that could happen is that you lose the channels that it's blocking.
When my interweb got hooked up, they put one on at the pole that blocks everything because I didn't get the cable service.

Yes, that is a cable trap. Cable companies use them to trap channels or internet service. Basically they trap out a set spectrum on bandwidth. I wouldn't hook it up to my cable service, you will end up trapping something out not enabling you to get more services.