It signals supermarket strike by third of September (5,4)

I believe the answer is:

aldis lamp

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'it signals' is the definition.
The definition suggests a singular noun which matches the answer.

'supermarket strike by third of september' is the wordplay.
'supermarket' becomes 'aldi' (German supermarket also operating in the UK).
'strike' becomes 'slam' (I've seen this before).
'by' means one lot of letters go next to another.
'third of september' becomes 'p' (ard letter of 'september').
'aldi'+'slam'+'p'='ALDIS LAMP'

Can you help me to learn more?

(Other definitions for aldis lamp that I've seen before include "shiner" , "Hence flashes with meaning" .)

I've seen this clue in the Sydney Morning Herald.

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