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.
Image copyright David Baldwin Night Photography