To use signals, you can use libspeedwm. Previously, speedwm-utils (part of speedwm-extras) would be used but that now depends on libspeedwm anyway. Using libspeedwm directly is the easiest option.
If you do not have speedwm-extras or libspeedwm, you can use the speedwm binary itself. The syntax is speedwm -s "#cmd:<signum>"
This option is not as solid though as signums can and will likely be moved around breaking your scripts. Therefore I highly recommend you use libspeedwm when writing scripts.