Here is another Arles coin with a dot on the other side of the obverse legend break. Also S✶AR mintmark...probably the same engraver.
Constantine I
A.D. 322-323
19mm 3.0g
CONSTAN-•TINVS AVG; laureate head right.
SARMATIA DEVICTA; Victory advancing r., holding trophy, palm branch, spurning captive std. on ground to right.
In ex. S✶AR
RIC VII Arles 257