The first instance I found was from October 13, 2014, in a project log for The Hackaday Badge, that says:
The badge must contain the string. "BSAPEDWLOVKTUB.YBKAB" on the silkscreen.
The second is from the Hackaday Links: October 19, 2014 summary, just underneath the announcement of the Hackaday keycaps that are coming to the store soon.
The third is from the Hackaday Links: BSAPEDWLOVKTUB.YBKAB summary, where it actually replaces "October 26, 2014" or "October 26th, 2014" in the title of the post.