can anyone identify.....

Is it possible something was splashed up from the front onto the exhaust? Since you don't seem to have any leaks that would be a guess, but to clean it off you may need something pretty strong.

Was it hot out? Looks like a bit of road tar that they use to fix cracks in the pavement.

I would suggest a lot of paint thinner to get that off of there.

I noticed yesterday when I fired the bike up to go out. nothing else is splashed and it was sticky to the the touch this morning.

If it is still tacky, it will be much easier to get off. Hit it with some paint thinner on a rag or a tire brush, and you should be solid.

If it's road tar WD40 will take it off.

I had a plastic bag blow up and do the same on another bike, a real bugger to shift! I used a craft knife, thinners, then a Scotch bright pad to recover the finish.