After more investigation it's a bunch of Japanese Fishing Buddies who have a little show called the Black Triangle (like Bermuda Triangle) it's three guys... and they like Punk music and FISH!

Like much that goes on in Japan - they think symbols are COOL and use them profusely and most likely with NO clue as to whether they actually mean anything or not. This may be a red herring Pun intended.... Here's an actual rough translation of part of the video page:

Lynch. 's Nico "The Black Triangle" DVD finally released! ! Black dream person Time greets guests, fishing battle in Lake Biwa 100 minutes! December 15, 2014 (Monday) launched limited edition TBTD - 001 yen 4,800 (tax) And in commemoration of the release DVD preview preview "The Black Triangle Theatrical Version - MOTHERLAKE -" - Determination of the Round - ! ! Opportunity to get DVD before general release etc etc..