Making a string appear conditionally (on the homepage)

Hi:

I’m toying with a plug-in that inserts code into wordpress pages depending on user settings.

It seems easy enough to inject it into specific wordpress pages based on their page ID #, but I was wondering, what about onto the WordPress homepage? Is there an action, for example, that I could tag that occurs only on the homepage, or is there some other method I could use to accomplish the same end?

Thanks.