I recognize what you mean about the office memos due to trivial misunderstandings (particularly tone misunderstandings) escalating. In my experience, almost all of them are the cases of someone erring on the side of seriousness. Myself, I mitigate that up front by judicious use of two emoticons: ":)" and ";)". The very act of using either of them, independent of the choice and context, already marks the whole sentence/paragraph/conversation as friendly.
Adding trees and rocketships and popcorns? Especially to either replace the exact word, or put it next to that word? What's the point?
(Ok, I'll admit I found two other emojis useful at work: thumbs-up and facepalm.)