What is sign for one breast is bigger than the other.

Could be normal: This could be normal if it has always been so.If you are not sure get yourself checked.

Likely normal: Realize it is very common for breast to be asymmetric. While things like infections, hormonal changes, cysts and masses (including cancer) can cause breast asymmetry usually it's very obvious that something concerning is going on if you can readily see a size difference. If you have no symptoms and the breasts feel similar it's most likely just normal.

In sign language?: One sign that a breast is larger than the other is that the larger one displaces more water if lowered into tub. Its called Archimedes Principle. I would not recommend that you do this out in the open at a department store if shopping for a bra. Sorry. This one had me stumped and this is the best I could come up with.