This client side mod allows you to paste special characters into the chat, on signs and in the anvil text box. Additionally, you can select a unicode font that is supported by minecraft, and your typed text will automatically get converted into the supported characters. All symbols are supported by minecraft, meaning everyone can see them, without needing the mod on their client and the server.
Some aspects of this mod are configurable using Cloth config (not required). The configuration screen is (for now only) accessible through the ModMenu config button. You can specify custom symbols in the configuration screen, which will appear in the last "custom" symbol tab.
On the top right of the chat screen, you can choose between multiple different fonts. Everything you type will get converted to that font, which makes use of unicode characters to produce a more interesting looking text.