MN sent me an email alert that I'd been mentioned in a post - presumably with the @ symbol.
So that appeared on my phone screen with my username visible - so could be noticed by my DC or conceivably my ex as he's sometimes around, who would then know my username and be able to search me!
I need to switch this off but also to alert mumsnet that doing this without warning could have serious consequences e.g. for those using MN for help with abusive relationships.