This varies across seasons.
In the first season, we get several clear shots of his uniform collar and shoulder epaulets: he wears the gold, irregular trapezoid insignia near his neck that all EarthForce officer ranks share, but lacks any insignia on the opposite end of the shoulder board; e.g., three diamonds to indicate a major, an irregular trapezoid with varying colours and number of bars to indicate Ensign, Lieutenant, Commander, etc.
After the uniform change we get a shot of him in formal dress, during which he appears to wear the insignia of a Lieutenant or Lieutenant Commander.