I've learned how to write in things, thanks to help from Unixmad...
In order to write things, you will need the inscription skill. (a pencil gives you this skill when you apply it, much like a talisman gives you wizardry when applied)
Then you need an empty book or scroll.
Place the scroll in your main inventory, and then mark it by saying "/mark scroll". Once you've done this, make sure you have readied the inscription skill, and then say the following to write into the scroll:
/use_skill inscription "text"
Replacing "text" with whatever you would like to write. This will write a passage into the scroll. You may write repeatedly in one scroll, however it will not erase or overwrite the previous inscription, it will continue like another paragraph.
Unixmad will be explaining how to use the "mark rune" spell to place signs or whatever using the spell. He should post about it sometime soon.