A parent who has no idea what discord is but sees this poster is going to get the wrong idea, be suspicious of their kid and their kid's computer use, get scared and react badly.

"Hey kid stop doing that, turn off the computer we're taking it away, I saw that on a police poster" is more likely.

You don't tell people to contact the police over innocuous stuff like this. It's ridiculous.

The police in the UK are institutionally ignorant of computers and computer use, and this poster is harmful.

(edit: Can you not see this for what it is? Fear and ignorance in poster form?)

(edit2: The NCA have said they were not involved in this poster. Looks like an ignorant local police/council screwup)