Can you be a little more specific with your question? There are at least 3 separate FDA regulations related to labeling (801, 809, 820) but 820 always applies and depending on your device 801 or 809 (or maybe even another regulation) will apply.
The 15223 standard specifies the symbols to use. If your label needs to convey the information for which a symbol exists in 15223, then use that symbol. In general, almost any ISO 7000 symbol is suitable, but start with 15223. Also, various standards include specific symbols (Annex D of 60601 for example), so pay attention to those, too.
You should have a specification document for the labels for your device, or else sprinkle the specs for labels to the applicable subsystem specs, such as packaging. Q: What does a label specification include? A: Content (words and/or symbol), but also dimensions, specific text, material, adhesive, radius of corners, etc. Each label should have a mechanical drawing with this information on it and each label will have a part number.
Just to piggy-back off tomshoup's excellent reply, there are other aspects regarding labeling that need to be considered. First, there's durability (there will be tests driven by 60601 testing to ensure the label holds up to indicated cleaning as well as the requirements in 820.120). Then there's control (label storage and labeling operations - see 820.120 also). And finally (although there may well be more things to consider that I'm not immediately thinking of), Unique Device Identifier (UDI) may be something you need to address.