Is Michaels a surname?
If not, where's the apostrophe?
Despite that, pleased that you have one!

I don't know. However, it is very common in the US for businesses to drop the apostrophe for a possessive. Probably something to do with making the sign look "cleaner," as if it would be a confusing and messy experience to read an apostrophe. Hence, Starbucks, Bealls, Penneys, a local store called Pinkys ( www.ipernity.com/doc/1227338/45995320 ), ad infinitum.

Thank you, Winscha!