custom or a custom

[RajuMV]

Friends,
Here is a sentence from the daily The Hindu, published today: Festive Faberge Eggs, custom designed by some of the world's leading artists and designers, are displayed at Rockefeller Plaza in New York in celebration of the Easter season.
I think indefinite article a is to be used before custom for the sentence to be grammatically correct.
Or before custom indefinite article is not used? please clarify.

Thanking you in anticipation

 

[sdgraham]

"Custom" here is not a noun

It would have been clearer with a hyphen.

Collins Concise English Dictionary © HarperCollins Publishers::

custom /ˈkʌstəm/adj

• made to the specifications of an individual customer (often in the combinations custom-built, custom-made)

 

[Copyright]

Think of it as a description of the eggs: Custom-designed Faberge Eggs. It has just been reordered, with "custom designed" as an adjective phrase, so no need for an article.

Added: Cross-posted with sdgraham.

 

[RajuMV]

Thanks a lot to both sdgraham and copyright