Service mark symbol. The service mark symbol (â ), the letters SM in superscript style) is a symbol used in the United States to provide notice that the preceding mark is a service mark.
Size matters: The micro and mini USB connectors are of similar width. But the micro connector is much thinner (smaller vertical dimension). Some product designs were not able to accommodate the height of the mini receptacle and the new thinner receptacle will encourage and allow thinner products.
Additionally, as most phones have micro-USB sockets, but most USB dongles have full-size USB plugs, as below many OTG cables have a male micro-B USB plug at one end, and a female USB-A plug at the other to convert between the different sized connectors.