If you really want the seams to show and want a neat finish. You could single crochet them together. You would have a wonderful raised ridge where the seams are and it would also be very neat looking.
Well crud, I can't seem to find anything on the net concerning single crocheting seams on knitted items anywhere. Well shucks, Hmmmm,
All I can think of doing is, get a crochet hook that is 1 or two sizes smaller than your knitting needle size, Use a contrasting color yarn or matching (depends on what you want the finished item to look like) and place squares wrong side together and right sides facing out, matching stiches on both pieces, insert the crochet hook in the end of the rows (each piece) and single crochet across. or if you are joining end to end then do the same thing (might have to adjust the amount of crochet stitches as they are a bit wider than the normal knit stitch) and just sc across, making sure not to pull too tightly or put too many stitches so that the piece starts to ruffle. That's the only thing I can think of. Sheesh, maybe I need to make a tutorial on my blog for seaming knitting with crochet etc. hmmm or maybe someone else can. It's a thought though huh?
Sorry I couldn't be of more help to ya