Hello Tony
I don't know signs directly receiving SIRI messages (also I heard of projects possibly going that way, but I don't know if they finally did), but we have more and more examples here in France where sytems driving the signs are fed by SIRI (available at RATP, INEO some SNCF stations, and more and more in Ile-De-France since the STIF, Authority for Ile-de-France, has made SIRI mandatory for all realtime inter-system exchanges).
Cordialement
Christophe