You need to set a texture in your server and edit the so called glyphs, when you have done that just get the glyph code and put in the String of whatever you want in your server. For example: I think that's a old glyph image of Hive and if you want to get the minecoin emoji just type \uE102 For each 16x16 pixel space in the glyph, you add 1 to the number going from top left to right, so like \uE100, \uE101, \uE102 etc \uE101 being the iron chestplate emoji and \uE102 being the minecoin emoji.
No problem and if you want to see more about it, I recommend searching for "Emojis & Symbols | Bedrock Wiki" in Google and you will have more informations about it.