Jeb's face changes way too quickly for him to read anything lengthy on that card. We know that symbolism will be their downfall, and the cabal/masons use quick hand gestures, covering of an eye, etc. to convey a message.

My guess is they have a symbol for "executed" or something similar. It would be a quick no brainer image for those in the know, and Jeb would have immediately understood how his father really died.