permissions for things like rpg servers would be nice like to allow only staff to place/make picture signs as this can obviously be a problem with everyone on the server being able to upload any image they want and have it visible to other players

Since there are requests from many server administrators, we are developing the spigot plug-in, SignPictureManager, which can restrict the installation of SignPicture. With knowledge of plug-in development, you can cooperate with development by pull request etc. Please cooperate if you are interested.
https://github.com/Team-Fruit/SignPictureManager

多くのサーバー管理者から要望があるため、私たちはSignPictureの設置を制限できるspigotプラグイン、SignPictureManagerの開発を進めています。プラグイン開発の知識があれば、プルリクエストなどで開発に協力することができます。興味があればぜひご協力ください。

thx for the update ill take a look at what u got goin.

Sorry for my late reply.
I made the first release of SignPictureManager.
https://dev.bukkit.org/projects/signpicturemanager

Much the same as was requested in #33 - any chanches we can get it for forge?