sidecar | = S = | sig block

SIG /sig/ n.

(also common as a prefix in combining forms) A Special Interest Group, in one of several technical areas, sponsored by the Association for Computing Machinery; well-known ones include SIGPLAN (the Special Interest Group on Programming Languages), SIGARCH (the Special Interest Group for Computer Architecture) and SIGGRAPH (the Special Interest Group for Computer Graphics). Hackers, not surprisingly, like to overextend this naming convention to less formal associations like SIGBEER (at ACM conferences) and SIGFOOD (at University of Illinois).

sidecar | = S = | sig block