Is there a RPN operation that does nothing? (NOP)

[tcab]

What is the best RPN command (for say, 42s/free42) that does nothing?
A NOP operation.

• Presumably setting or clearing a flag that nobody uses would do the trick - but strictly speaking has a side effect.
• Two X<>Y operations would work but that's two operations, not one.
• A label would work, but I don't want to use up a label or imply there is a related goto somewhere.
  

Any ideas?