This amulet with thumb between first and second fingers seems to have a sexual connotation1. The clenched first, mostly in blue glaze, appeared in the Roman Period1
Blue glazed right clenched fist H 2.6, W 1.3 Roman Period © 2017 University College London LDUCE-UC #38466
Blue-green/yellow glazed right clenched fist H 1.6 Roman Period Museo Egizio #1217
Blue/green/yellow glazed left clenched fist H 1.5, W 0.5, D 0.5 Roman Period Museo Egizio #1219
References
1. Petrie W M F. Amulets, 1914, p. 11 and Figs. 13a,b