OK, so if you 'mixed them together' then 'telling them apart' would be virtually impossible, since they are chemically very similar and at this point would be mixed. Something like FACS might separate out the cells, but I don't think that is what you are getting at.
So, let's put this another way -- if you took two separate stains, one of pig blood and the other human blood, then it would be VERY easy to tell them apart. A simple ELISA-type test (using an antibody against human blood hemoglobin, for instance) would be the quickest and easiest way. See more info here:
Independent Forensics DNA Testing and Technologies . Genetically they are also very different -- a simple battery of STR tests could very quickly tell you which was the human and which was pig.
On the other hand, there are a great deal of genetic similarities between pigs and humans. Many of the proteins are quite close in sequence and structure, etc. Genetically, this is just a guess, but I'm imagining there is probably around 60% similarity at the genomic level (give or take an order of magnitude :-)).