I did not make up the acronym, I have to attribute that to my colleague, but here's a post on a new warning device in downtown Portland.
This "Bus Only Activated Transit Sign" (BATS) was activated by the City in cooperation with TriMet at their request. The intent of the sign is to warn pedestrians traveling in the east-west direction on Burnside of a bus approaching from the left turn (westbound direction). The warning sign is a caution indication designed to support the pedestrian indication as this is an area where TriMet has complained of a considerable amount of people walking in front of their left turning bus when they have a Don't WALK indication. Part of the "problem" in downtown is that there it is mostly just two phase intersections, so a left turn crossing maneuver is a bit of an anomaly. in most intersections, there isn't the expectation that this left turn conflict will be experienced and this one is particularly intermittent since it is a bus only movement and it only is active if a bus is present.