c-comment-only-line-offset

c-comment-only-line-offset is a variable defined in `cc-vars.el'.
Its value is

set-from-style

Documentation:
*Extra offset for line which contains only the start of a comment.
Can contain an integer or a cons cell of the form:

(NON-ANCHORED-OFFSET . ANCHORED-OFFSET)

Where NON-ANCHORED-OFFSET is the amount of offset given to
non-column-zero anchored comment-only lines, and ANCHORED-OFFSET is
the amount of offset to give column-zero anchored comment-only lines.
Just an integer as value is equivalent to ( . -1000).

Note that this variable only has effect when the `c-lineup-comment'
lineup function is used on the `comment-intro' syntactic symbol (the
default).

This is a style variable. Apart from the valid values described
above, it can be set to the symbol `set-from-style'. In that case,
it takes its value from the style system (see `c-default-style' and
`c-style-alist') when a CC Mode buffer is initialized. Otherwise,
the value set here overrides the style system (there is a variable
`c-old-style-variable-behavior' that changes this, though).

You can customize this variable.