Ivo,
With several people putting together pieces of information, we've managed to identify the maker as Illinois Pacific Glass, circa 1932. The company appears to have only made bottles and jars, so it was probably a special container intended to be kept as a vase after the contents was used, but I've had no luck figuring out what the contents might have been. Letters in the triangle are either IPG or IPC since the company used both. The I and P lean to the right, and the last letter leans strongly left, which is part of what made them hard to read.