Representations of gestures can be trademarks.  For example Facebook’s Application No. 85020073 covers a depiction of a thumbs up gesture followed with the word “LIKE” in a rectangle:

However, Reg. No. 4735632 arguably covers a gesture itself (“The mark consists of a thumbs up hand gesture with the thumb having a face wearing a ninja mask.”):

There is precedent for gestures being a mark: Reg. No. 2520312 (now expired) covered the sign language symbols for the numbers 2520; Reg. No.  2643221 (also expired) covered the sign language symbol for C; Reg. Nos. 1350018 and 2028426 (also expired) covered the sign language symbols for H and D.

If 15 USC 1052(a)’s prohibition against the registration of “immoral, scandalous, or disparaging marks” is affirmed as unconstitutional, one has to wonder what kinds of “gestures” might be registered as trademarks and service marks.