Reddish-brown pottery

If it was fired in a kiln, it certainly can go in the oven. If it is glazed in lead-based, I wouldn't eat out of it. 2 questions for you to ask before purchasing?

As I mentioned earlier, it's OK to put in an oven but, to be safe, put it in a cold oven to avoid shock and cracking. As to glazes containing lead: I'm a potter and don't use these on my wares, but I do - on occasion - eat out of vessels which have been lead-glazed ( but only non-acidic foods) and many people still do on a daily basis, since most low-fired ware in Mexico is still glazed this way. Reasonably inexpensive lead testing kits are available.