The Stars and Stripes guidons came into use in January 1862 via a general order. Artillery batteries got them as did cavalry companies. While I cannot prove it, the flag with the "B" on it could well have come from that Indiana cavalry unit but just as well could have been from the artillery as well. If that battery was part of a larger battalion as Battery B (and then their name and designation) that also could be its ID.

Greg Biggs