When discussing details for any coin, which side is left or right? When looking at a coin, it's left side (to our view) is the coin itself's right side. This is driving me nuts when describing a coin.
I agree with @masterswimmer above. In the numismatic literature, I always see references to "clock face" (e.g. "...at the 8 o'clock position near the rim on the obverse one finds the privy mark of the Paris Mint..."). Also, if referring to the "right" or "left" of a device on the coin, I've also read things like, "...the eagle's right talons clutch a globe, while the left talons grip a sheathed sword..."
Clock face terms are more precise, but normally I see coins described from the viewer's point of view, so that "head left" means the head of Athena or whoever is facing to my left as I look at the coin.
Convention is the observer's POV., unless otherwise specified. Also, clock face convention is, for example, K10 for ten o'clock.
You can also use port and starboard. And "bite me" for any objections. RPM's use N, S, E, W or NW etc. to describe the position shift of the repuch. They're kind a small for a clock position.