A walrus signalling (5)

I believe the answer is:

morse

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'a walrus' is the definition.
(I've seen this in another clue)

I can't explain the remainder of the clue.

(Other definitions for morse that I've seen before include "Code inventor, Samuel" , "10 [SLEUTH]" , "& 24 Across Encrypted language" , "used to transmit messages" , "Walrus - TV detective" .)

I've seen this clue in The Globe and Mail.

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