Costers’ companions? (7)

I believe the answer is:

escorts

I'm a little stuck... Click here to teach me more about this clue!

'companions?' is the definition.
(escort is a kind of companion)

'costers'' is the wordplay.
'costers' anagrams to 'ESCORTS'.
Though, I'm unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for escorts that I've seen before include "Accompanies, perhaps socially" , "Accompanies to protect" , "Armed guards" , "Attendants" , "They accompany others" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app