Because Constantine was both practical and an opportunist, I doubt he would have done anything to antagonize the majority of his army who were Pagan. He could, however, have opted for the Chi-Ro symbol since it predated Christianity and would have been accepted positively by his Pagan troops.
Here is a coin from Ptolemy III (246-222 BCE). Note the Chi-Ro between the legs of the eagle.
Pagan Greek scribes used the Chi Ro symbol to mark portions of papyri texts they deemed important.
Maybe not too surprisingly, however, the vast majority of coins from Constantine did not have Christian imagery.
Interestingly, the Arch of Constantine, which commemorates Constantine’s triumph at the Milvian Bridge, does not depict the Chi Ro symbol.
https://coinweek.com/ancient-coins/ngc-ancients-late-roman-coin-reverse-types-part-2/
http://www.constantinethegreatcoins.com/symbols/