This question came in recently:
"I was wondering how I get dried glue off belli button rounds"
Here's my overlong answer:
It depends on the type of glue that's on them. (I'm also assuming that the tile are loose and not part of a mosaic piece.)
If it's a water-based glue (Weldbond, Elmers, Tacky Glue) you can put them in water and soak them until the glue turns white and wipe it off.
Solvent-based adhesives (silicone, E600, Dazzle Tac) you can scrape off with a knife.
Cement-based adhesives (thinset, concrete, mortar) you will want to chip off with a hammer or dull cutting tool. You can also find products that will eat away at cement at hardware stores.
If the glue is on the face of the tiles in your finished mosaic piece, you can just scrape it off with a knife. I keep a dull Exacto knife on my table for this, along with other uses.