I think this is the second thread we've had about this in the past two weeks. I urge you to search next time before posting a new thread.
edit: here's the thread from a few weeks ago -
other drugs on blotter
Any drug thats dosing range is between <.5 - 2mg can fit on blotter. (although yes there have been cases where blotter contained dosages of much higher [cases of DOM blotter and 2C-C blotter])
DOx chems can fit on blotter (DOB/DOI/DOC/etc)
5-MeO-aMT can fit on blotter
Some benzo's can fit on blotter (like Phenazepam, Alprazolam, Clonazepam, etc)
Its very possible your friend's connect could be selling adulterated LSD blotter as RC's are easier to get a hold of and are commonly used (specifically DOx chems like DOB) in place of LSD and sold as LSD.
There really isnt any way to be sure (although some have mentioned LSD testing kits. Not quite sure how accurate those are though as ive never tried 'em).
Most say taste (although that's no true means of identifying a chem).
The only way to really tell is to be a lab rat yourself, so if you're really not sure that your friend's connect is selling LSD but rather some sort of RC, dont take the blotter.
Its your choice, really.