The most common and most likely answer to this crossword clue is the 8 letter word METHINKS
I've seen this crossword clue in The Guardian
M
E
T
H
I
N
K
S
More clues leading to the result METHINKS
- One liquid drops into another, yours truly imagines
- My opinion is old-fashioned
- Satisfied with hotel signs I would say
- Drug makes writing bolder one supposes
- I believe printing stuff in spirit
- I believe spirits may pen writing
- I feel the faux furs should be worn
- Alcohol restricts the source of one’s writing, according to author
Buddy explains!

The straight part
We know that "I believe" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case i believe = methinks.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.