The most common and most likely answer to this crossword clue is the 3 letter word ADS
A
D
S
Buddy explains!
The straight part
We know that "They are for promoting" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case they are for promoting = ads.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does ADS mean?
ADS noun- Advertisement.
- Advantage
- (debating) advantage