For the Gid, who was pretty flabbergasted by this, I present a couple of photos of the phenomenon.
The first used to be a grave marker; a neighbor rescued it from the scrap heap and it's now in my possession. Note the vegetal motif. This one's been re-painted with rust-proofing paint.
The following image comes from Le Burgaud, a neighboring town I've mentioned previously; in this town there is a small chapel dedicated to Notre Dame de Aubets along with a sacred spring. This second example is particularly striking. The vegetal motif on the cross is less abstract and the cross itself like two logs lashed together.
A lot could be said on this topic but I've written so many things about Marial shrines lately I'm totally fuggered on it. Suffice it to say that's it's pretty clear evidence of the thriving cult of Mary in France and may have something to do with pre-Christian goddesses of the crossroads such as Hecate and the Mater Larum, both of which, like Mary in the Cross (usually found as a grave marker--exhibit A--or crossroad marker--exhibit B), have associations with the afterlife. (previously).
Make of that what you will.