There are two distinctive faces on this side of the monolith (shown below). I suspect that these distinctive balancing faces may represent a version of  the "dual symbol" that is, I realise, a common artistic and spiritual motif at Avebury. You can read about my discovery of dual symbolism by clicking here.

1.   Left Profile Face

2.   Right  Profile Face

This is clearly a "D" shaped face, a rounded profile with a distinctive eye, again a common Avebury motif.