LPR
This signature detects Line Printer Daemon Protocol (LPD), which is a set of programs that provide printer spooling and network print server functionality for Unix-like systems. It is old-style UNIX printing. LPD usually listens on TCP port 515.
Available to all SRX running 12.3X48+
Available to all MX running 20.2R1+
Available to all vSRX running 20.3R1+