It can be difficult to spot, even for moderators as the main reason we know each other is through NHS circles and the NHS Net VPN that we all have on our iPads polls out onto the Internet through proxy servers, or put another way, one of half a dozen static IP addresses.
If moderators ever start moderating, (and after Musket emailed me the contents of a PM he had recently from Joe Offer, I doubt there is hope..) then there would be no need for this.
I notice Ian uses Musket occasionally in music threads. I use my other log in for decent debate.