Hi!
First I like to thank you for this wonderfull addon!
One thing I realy missed as a feature: Other Icons then just the raidmarkers. In regard to the concept of plugins, I thought to write my first Addon ever, to add this feature to HandyNotes.

By doing so, I've run into some difficulties, to add this feature as a plugin. However, I managed to make it work on my now a little bit hacked version of HandyNotes. I've written a HandyNotes_Icons addon, that adds the ability to add icon packages to HandyNotes and allows to select, which icons to use and to change the descriptive text of the icons. To have actual new icons, one has to install then the icon packages he likes. This would also allow others, to create their own icon packages and share them with the community.
I've created projects for this on curseforge, where you can take a look at it if you like:
http://wow.curseforge.com/projects/hn_icons/
http://wow.curseforge.com/projects/hn_icons_misc/
http://wow.curseforge.com/projects/hn_icons_numbers/

Now to my actual request: I'm very new to prgramming addons, so I don't know, if I just don't see a possibility to add this functionality to your original code. If there is one, I would be very thankfully, if you could show it to me. If this is not possible, then I have found a simple way, to add the possibility to HandyNotes. On my hacked version of HandyNotes this seems to work without errors and does not make the original code any larger. But I must admid, that I did not read all your code, so it can be, that this does some harm somewhere. Here is what needs to be changed:
All references to the local variable "icons" in handynotes_handynotes.lua needs to be replaced with the reference to the variable "HN.icons";. This are actualy just 5 places:
33: "local icons" --> "HN.icons";
43: "HN.icons = icons" --> delete
141: "icons" --> "HN.icons";
280: "icons" --> "HN.icons";
297: "icons" --> "HN.icons";

Would this be possible? Of course I understand, if you don't like to change your code for some other addon, over which you have no control nor know its author.

Thanks in advance, for reading through my jolty english,
dickloraine