also piggie, "a little pig," by 1700, from pig (n.1) + -y (3). Related: Piggies. The piggy bank was popular from 1940 (ceramic or tin pig banks are noted by 1903 in American English, sometimes as souvenirs from Mexico).
The dates seem too early for this to be a source of that, but Scottish and Northern English pig (of unknown origin) meant "earthenware pot, pitcher, jar, etc." (mid-15c.), and in Scottish dialect pirlie pig (1799) was "small money box, usually circular and made of earthenware."