Negative guard took front off road sign (2,5)
I believe the answer is:
no entry
'road sign' is the definition.
(I've seen this in another clue)
'negative guard took front' is the wordplay.
I cannot really see how this works, but
'negative' could be 'no' (no is a kind of negative) and 'no' is found within the answer.
The remaining letters 'entry' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
'off' is the link.
Can you help me to learn more?
(Other definitions for no entry that I've seen before include "street sign" , "Admittance prohibited!" .)