Of course you can post your coin anywhere...it is important to get a second opinion, especially as I can be (and have been) wrong.
Yes, S is not possible, but a poorly preserved B can resemble an S. There is also the mintmark, without even being specific, it seems there are three objects, which fits for Rome, but not other mints. As far as the gamma being too big, you can compare with other examples. What one wants to see as an M in the left field, is what I see as a gamma and the spear.
below are some examples of Rome 258 for comparison