Enter an “X” in adjacent cell, same row. Insert column if there is not a suitable one available.
No additional bookmark needed. The X’s provide the visual clue. You can use
up to locate the end of (and gaps in) the X series in the column. If you have lots of gaps, an autofilter may also be useful.
If you really need a clearer visual clue, some kind of conditional fomat may be of use. You can also enter personal info in
Options.... When Calc knows who you are, it will remember your last edit and bring you back to that spot. Post a comment with some detail if you need more than this.