Only "Ensign" is available it seems. I had assumed that once you were promoted, a new "Lieutenant" option would appear from the Tailor's drop down menu, but all it has available is "Ensign" and "None".
Looking around, the only Starfleet officers with a displayed rank higher than Ensign (1 bar or pip) are the NPC's.
Submitted a bug but just wondering if anyone is able to display a Lieutenant's rank (or higher) on their uniform. I'm sure it can and will be added later, but kinda disappointing it's not in game at the moment. Or perhaps the rank insignias are present, just not working correctly on the Tailor display.