This half dollar has a very weird mint mark FG the G you can see but you barely can't see the F the f is lower than the g also. I'll try to get closer images of it
The "Weak FG" is caused by a grease-filled die and is very common. Also, the "F" on your coin is not lower than the "G". I think you're mistaking that small mark for the crossbar. I can see the top of the "F" in your close-up. The only two years that I'm sure are missing the "FG" due to an over-polished die are 1972D and 1982P. Chris