Yes, it's been possible since the Core30 release in October. We're getting close to fixing it with BIP110

Thanks but we meant on nodes already running BIP-110

BIP110 does not protect against it until activation.

Much clearer now thank you Luke. For noobs like us; signalling literally means: 'declaring that you will run node/s implementing BIP-110 when the time comes' So even if we are currently running Knot-BIP-110 version, no actual filtering is happening until activation. It's a declararion of intent at this stage.