The most common and most likely answer to this crossword clue is the 10 letter word EMBLAZONED
I've seen this crossword clue in The Daily Telegraph
E
M
B
L
A
Z
O
N
E
D
Buddy explains!

The straight part
We know that "Decorated" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case decorated = emblazoned.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 EMBLAZONED mean?
EMBLAZONED verb- To adorn with prominent markings.
- To inscribe upon.
- To draw (a coat of arms).
- To celebrate or extol as with deeds or merit.