soak them over night and there should be a smallish circular mark on one side this is the top. failing that plant them on their edge. Dont worry they will right themselves in the soil as they grow.

A well know gardener once did a trial, some bulbs the right way up and the rest up-side-down, they all flowered the same time.

Didn't work for Anemone coronaria when I did an involuntary trial--all the upside-down ones rotted!