I'm a fan of Blue Mountain Pottery, and love coming across it. It's not as popular as McCoy or Roseville, I've seen it mis-identified a few times. Since it was a Canadian Pottery company, that might be the reason for some of the confusion. Unfortunately, it closed it's doors in 2004, a victim of cheaper imports. It was a popular pottery company, and there are plenty of pieces in good condition, as well as fan clubs that can help you should you have any questions. However, as time goes on it will become more unique.
The glaze always catches my eye, and I check the item out. If it's the real deal, the glaze is thick, and Blue Mountain Pottery did a double glazing with two different colors known as "reflowing decorating." Some of the pieces with a closed bottom are marked BPM, but other marks existed. The most popular color is the greenish shade(s), but they also did other colors, such as reds and golds. They did figurines to serving ware. Below are a few pieces from my own collection, and they aren't for sale.
This is an example of the open bottom, it won't be marked. One of my pieces still has a paper label, but just because it isn't marked doesn't mean it's not Blue Mountain Pottery. As with anything, there are fakes, so be cautious and know the dealer.
This cat is approximately a foot tall, I couldn't get him in the entire photograph. Please note the label. With vintage, it's not tacky at all to leave the label on, and it increases value.