This thread is the highest Google result that's still not closed, so I'll necro it for future searches: @{pbd_safe} is a suffix Attribute for use with the variant Proficiency Dice rule from the DMG: Proficiency Dice This
optional rule replaces a character’s proficiency bonus with a
proficiency die, adding more randomness to the game and making
proficiency a less reliable indicator of mastery. Instead of adding a
proficiency bonus to an ability check, an attack roll, or saving throw,
the character’s player rolls a die. The Proficiency Die table shows
which die or dice to roll, as determined by the characte r’s level.
The default value once the Variant rule is selected is merely a Critical Success/Fumble removal: pbd_safe = cs0cf0 So you can safely leave it out of your custom macros if you don't intend to use this rule. I couldn't find this answer anywhere else, it might be buried somewhere though!