The most common and most likely answer to this crossword clue is the 5 plus 5 letter word LOYAL TOAST
I've seen this crossword clue in The Daily Telegraph
L
O
Y
A
L
T
O
A
S
T
More clues leading to the result LOYAL TOAST
Buddy explains!
The straight part
We know that "show of patriotism" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case show of patriotism = loyal toast.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.