The most common and most likely answer to this crossword clue is the 4 letter word PLUS
I've seen this crossword clue in The Times
P
L
U
S
More clues leading to the result PLUS
- Benefit of luxury slightly reduced
- What could be indicated by the sign of the cross
- Promotes eradicating source of Government benefit
- Luxury’s endless advantage
- An advantage being very rich, mostly
- With luxury, no husband needed
- Luxurious hotel’s abandoned asset
- Tops in Premier League, American, also
- Tea in angel's cup different — though in essence it's the same
- Do guests break up lesson?
Buddy explains!

The straight part
We know that "What could be indicated by the sign of the cross" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case what could be indicated by the sign of the cross = plus.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 PLUS mean?
PLUS noun- A positive quantity.
- An asset or useful addition.
- A plus sign: +.
- To add; to subject to addition.
- (often followed by 'up') To increase in magnitude.
- To improve.
- To provide critical feedback by giving suggestions for improvement rather than criticisms.
- (sales) To sell additional related items with an original purchase.
- To frame in a positive light; to provide a sympathetic interpretation.
- (social media) To give a mark of approval on Google+.
- To increase the potency of a remedy by diluting it in water and stirring.
- (optometry) To increase a correction.
- Being positive rather than negative or zero.
- Positive, or involving advantage.
- Electrically positive.
- (Of a quantity) Equal to or greater than; or more; upwards.
- And; sum of the previous one and the following one.
- With; having in addition.
- And also; in addition; besides (which).