What efforts are these? All I've seen are checkboxes on their web site making the user tick a box confirming that they aren't a US citizen.
Geo-blocking US IP addresses won't work either, because an ethereum contract can't refuse a transaction based upon its source IP address (it doesn't know it). So if an ICO publishes their ethereum contract address online (e.g. via a twitter post), they are implicitly advertising to US investors.
Geo-blocking US IP addresses won't work either, because an ethereum contract can't refuse a transaction based upon its source IP address (it doesn't know it). So if an ICO publishes their ethereum contract address online (e.g. via a twitter post), they are implicitly advertising to US investors.