MV is mounted Volunteers and TM is Texas Militia, which is the same thing as Texas State Troops. By law the TST were only for defense of the state, so they never left Texas. Their camps were mostly likely in the Militia districts which they were from. The 14th Brigade was from the Militia district that included Fanin and Hunt Counties. Your ancestor most likely was in the 1st Infantry Regiment, 14th brigade, Texas State Troops.