I have a legally registered Thompson M1A1 submachine gun with 204 TS Solomon placed on the left side of the weapon. Wondering if the armed guards assigned to liberty ships were issued Thompsons?

I am thinking the 204 is a rack number and was assigned to troop ship Solomon? This weapon was amnesty registered in 1968 but would love to know why someone put 204 TS Solomon on the weapon. Thank you.