I was looking at the badges page and noticed this in the sidebar:
Looking more closely, I discovered that these strange marks come from this user. Because they have a Zalgo-text username, it can often interfere with other text on the same page. E.g. on one of their questions:
Is this enough of an issue that the moderators should step in and edit the Zalgo text out of this user's name?
My personal feeling is that although this particular instance is fairly harmless in itself, allowing Zalgo text in usernames could set a dangerous precedent, as seen in this case from another site.