An example

Following define a sign with name piet:

sign define piet text=. linehl=Search texthl=Search

Note that linehl=<groupname> is used to highlight the whole line. We may define a new group using following command

:highlight <groupname> ctermbg=darkred guibg=darkred

Then using the command :sign place to put a sign

:exe ":sign place 2 line=104 name=piet file=" . expand("%:p")

Conclusion

It is possible to use this feature in the plugin. However I am not sure how I could use the feature without the sign character in the beginning of a line, which is a bit annoying.