Since VanishNoPaket has added the invisibility status notification using the Minecraft plugin channel, it's now possible to use this information within a client mod to know if you're vanished or not.
This Mod will create a Invisibility Potion IV effect while you're vanished.
You may also want to display the potion directly on your screen without the need to open your inventory every time. Here's a nice other client mod, doing this: StatusEffectHUD