It's just albumin, a protein, plus a little blood and fat and usually whatever else may be on the outside of your meat. It just looks gross and won't hurt you :) Just skim it off if you don't like it. This usually occurs more when you're making a stew or a soup - or if the meat has been frozen and then popped into a pan. If the meat is fresh and you're using a hot pan you shouldn't get the reaction as the hot pan will seal everything in. I know some people rinse and wipe their meat, oh that sounds bad - sorry, to get whatever is on the surface off but they'll still leave the resulting "scum" as they feel there may still be nutrients in there.

That scum is delicious! Seriously, try separating it off like you probably already do... and then eat it all! If you can get past the appearance, you might start thinking that it's the best part of the meat.

And yeah, I think it's blood.

I'm indifferent about the scum. I mix it in with the beef and don't know it's there.