The good news is that I think I've found your pin!

[PDF]Civilisations de l'Europe au Néolithique et à l'Age du bronze ...
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... Les épingles à tête en marteau (ou en béquille), connues dans la culture ... crosse
», « objet » triangulaire, poignard, arc et flèches, hache, etc.) qui n ...
www.college-de-france.fr/media/civ_eur/ UPL51953_GuilaineR01-02.pdf

The bad news is that this is a descriptive term, so I'm not sure you're going to find an exact match. I'm suggesting "hammer head," based on the French description, above. Here are some Neolithic period pin descriptions which would suggest similar shapes–and some descriptions of bone pins with similar shapes:

Poulnabrone Dolmen
... The remains of up to 22 individuals from the Neolithic were found. ... 2 stone beads,
a decorated bone pendant, a fragment of a mushroom-headed bone pin, 2 quartz ...
www.nd.edu/~ikuijt/Ireland/Sites/ cquinn/poulnabronedetail.htm

One specific group identified is the conical headed bone pin, an element of the Linkardstown burial tradition (Raftery 1974; Manning 1985). This one has 4 drawings of the pins, which have two heads.
http://www.ucd.ie/~trowel/murray.htm

This one, made of reindeer bone, also illustrated, shows what could be described as a crutch "head," does not have a hammer head shape at all!

Here's the description - see the URL for the illustration:

The complete perforated bone pin (Figure 5 above), made on a split roe deer metatarsal, is 148 mm long and is 15 mm wide at the flattened proximal end, tapering distally to a finely worked point with a cylindrical cross section. The proximal end incorporates a smooth unmodified portion of the articular surface of the metatarsal. The drilled perforation is 2 mm in diameter and is positioned 10 mm from the proximal end. The pin appears to have been crafted using stone tools, and it is comparable with similar artefacts found in Bronze Age burial mounds in Derbyshire and in East Yorkshire. http://www.shef.ac.uk/~capra/1/carsing.html.

The photo at this URL shows a smallish two-headed bone pin beside the skeletal remains: http://www.cilnews.unige.it/archeo/f027.htm

This pin, found in Scotland, probably looks like the reindeer one:

Other archeological finds were, a bone pin with eye http://www.highlanderweb.co.uk/haunted/haunt11.htm