When we find a stone hand tool, the first thing we do is look for the handhold.  As you are rolling these around and switching between hands, checking to see which grip feels the most comfortable, some markers allow you to eventually decide on the best fit and handedness.  That is not to say that all of these are either left or right-handed (many of our hand tools show use by both hands), but some of the design choices were obviously made with a specific hand in mind.   Two terms I use to describe a couple of these markers are "clips" and "mesas".

"Clips" are short sides at the top of the tool.  These seem to be crafted to allow the user to curve the index finger over the top on the smaller, thin tools for added stability.  We also see clips on larger and thicker tools, usually on thumb sides and occasionally for a handhold.  "Mesas" are a flattened clip to allow an index finger or thumb to rest on top of the tool for extra control, and we see them also used for handholds on larger tools.  Here's a gallery of clips and mesas.