MER: ME ligated; trio of pellets arranged in a triangle, above and below legend.
Reverse
Lightning bolt.
Reference
Dissard, P. 1905. Collection Récamier. Catalogue des plombs antiques (sceaux, tessères, monnaies et objets divers), Paris and London: Rollin et Feuardent, https://zenon.dainst.org/Record/000740205
Lang, M. and M. Crosby (1964). The Athenian Agora X: Weights, Measures and Tokens. Princeton, New Jersey, The American School of Classical Studies at Athens. (https://zenon.dainst.org/Record/000211771)