The one which appears when one right clicks the bookmark margin in Picaxe editor.Which "bookmark" are you referring to ?
Thanks Hippy - I'll give it a go.That sets a visible marker in the line number column so they are easy to spot when scrolling through the program.
Ctrl-D can be used to jump down to the next bookmark and Ctrl-U to jump up to the previous bookmark so you can quickly jump between various bookmarked parts of the code.
They are analogous to placing bookmarks in an actual book so you can quickly goto to particular places in the program code.