Constantine, AE follis, Rome, 320 AD.

CONST-ANTINVS AVG, helmeted, cuirassed bust right.
ROMAE AETERNAE, Roma seated right, holding shield on
knees inscribed XV.
Mintmark R epw CT.

RIC VII Rome 194 corr.
On his website of Constantine coins, Victor Clark writes:

Part of this mint mark is a cryptogram, and is Greek for 
Eros, which in Latin is amor. 

Contributed by Doug Smith, Oct. 2012.