idle curiosity about "guest" numbers

Not really sure where to post this, so feel free to move it if you think this is the wrong place for it.

I was just wondering, when you look at the front page and see something like "In total there are 156 users Online :: 6 Members and 150 Guests ", is there any easy way to know how many of those 150 are people and how many are bots of some sort?

It's just idle curiosity on my part, so if it's not easy to distinguish them then don't worry about it.

'bots and unsigned members I'd guess.