Behold the Brostika! Like the hidden arrow in the FedEx logo, Slack's new brand has a negative-space surprise in store. The bars point the "lucky" left way, at least, rather than, well, to the right.
Here it is with the negative space filled in:
Below are Slack's "Logo explorations for the octothorpe." Octothorpe is a fancy word for the pound/hash symbol, which they have somehow managed to turn into a contact sheet of procedurally-generated swastikas.
UPDATE: T. Carter Baxter nails it better than I:
I know people at Slack, and I know they're smart, capable and caring people. But once you hear "swastika made of dicks" it's kind of over for the new logo.
— T Carter Baxter (@tbaxter) January 16, 2019