By filling in the stone pores, resination in effect seals the stone.  While not the intent, it is a very attractive and useful by-product.  If your counter has been fabricated in the past five years there is a very good chance that it was resinated, as this process has become mainstream.  How do you tell?  Unfortunately there is no sure fire way of being sure that is non-destructive to a finished counter.  If we were looking at slabs in a fabricator's slab yard you might see residual drip marks along the side of slab or on the underside, however the absense of such marks does not mean the stone was not resinated.  When in doubt seal.  If you know who fabricated your counters ask them.  They can typically provide you guidance on whether stone coming from your stone's quarry are being resinated or not.