"Perforated" or "Pierced Batons" (in French "bâton percé") are man-made historical artefacts formed from deer antlers. They have been found widely distributed across Europe, and range in age from around 23K to 12K years old. They are typically 'Y' or 'T' shaped, and all feature a carefully drilled circular hole.

Their function is unknown. Theories include uses as :

• Arrow or spear-straighteners
• Spear throwers
• Fertility symbols
• Phallic symbols
• Dress fasteners
• Calendars

A 2019 study found that they were "clearly used as tools as demonstrated by extensive use-wear on the perforations’ edges and ancient fractures across both the distal parts and the shafts."

Noting, however, that :

Despite the large number of batons found (> 400), their use still remains enigmatic. No fewer than 40 functional hypotheses have been proposed, following debates that have persisted for over 150 years; the perforated baton has consequently become emblematic of our misunderstanding of some ancient objects’ functions.

Source : Archaeological and Anthropological Sciences volume 11, pages 5231–5255 (2019)

Further reading Wikipedia