Sparschweinchen is just the diminutive of Sparschwein "piggy bank".

I'm not sure whether the typical German-speaker would be more likely to intepret Schweinebank as a bank for the use of pigs or pig-farmers (cf. Schiffsbank, Bauerbank) or a bank for storing pigs (by analogy with Datenbank). I think the latter, but either way, hilarity ensues.

You think that's bad, Bengt, bikerbaer was once quizzing a student on the parts of a car and his answer to the question, "If it were dark, you'd turn on your..." was "Schweinwerfer!"