There probably isn't a central database to verify against so the solution would be to come up with a distributed system where each country implements its own verification process and then implement a standardized messaging structure that all countries would have to use. It would be a significant development effort to make something like that and it probably wouldn't pay off to if it was made just for citizens initiative. Considering in the last 5 years there has been only 4 (5 if we also count SKG) initiatives that have passed 1 mil it's probably cheaper to collect all the signatures and then have each country verify the dataset that relates to their country.