The most common and most likely answer to this crossword clue is the 8 plus 4 letter word PLIMSOLL LINE
P
L
I
M
S
O
L
L
L
I
N
E
More clues leading to the result PLIMSOLL LINE
Buddy explains!
The straight part
We know that "Indicator of successful flotation/footwear brand" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case indicator of successful flotation/footwear brand = plimsoll line.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.