Since snapshot 20w17a (pre 1.16) Minecraft is supporting full Unicode range allowing the use of emojis in all places like chat, books and signs. Sadly Minecraft's own font didn't got an update so I did it myself with this resource pack.
I recommend using an online tool like Twitter Symbols to copy/paste emojis into Minecraft.
&f for white).§f into the book followed by an emoji. Copy/paste §0 to get black again, else normal font could be a bit hard to read.
