Hear it from us first
Get a mail when your network starts sending something that doesn't belong on an IXP peering LAN: router advertisements, spanning tree, DHCP, discovery protocols, stray broadcast. With the frames as a pcap, and another mail when it stops.
We use PeeringDB to check which networks you're affiliated with. Alerts are free for networks bgp.tools tags as personal, and a paid option for everyone else.