The convention for distinguishing genes from proteins seems to vary from journal to journal, so stick with whatever seems to be used in the journal you're most likely to publish in. Usually, genes are lowercase with or without italics, and proteins either start with a capital letter or are in all caps, but this isn't really done consistently all the time.
To distinguish proteins of different species, a lowercase letter in front of the protein abbreviation corresponding to the species is used. So, for something like prolactin, which is abbreviated PRL, for mouse you'd use mPRL (m is for murine, not mouse, incidentally), hPRL for human, ePRL for equine (horse), oPRL for ovine (sheep) rPRL for rat, and I'm not sure how you'd distinguish rat from rabbit, or anything else you start getting repeats of these letters for. I don't think it's a standard convention, but in our lab, we use two letters for some species to clarify this, since we work with proteins of many species. So, rt is for rat and rb for rabbit. It's not perfect. When in doubt, write the whole word out. For our lab, we just all use the same convention within the lab to avoid confusion, but write out the full word for publication and define any abbreviation as we would any other abbreviation.
I like the system used by the folks working with fruit flies! Basically, just pick a fun name that doesn't mean anything, just a good abbreviation that's fun to say. Considering how often a newly discovered gene or protein turns out to have a completely different function from what is initially thought, it saves a lot of trouble with names that don't fit the function. And it's better than naming things after the discoverer too...besides, that only works for the first thing you discover, then you still have to come up with new names after that.