It's not clear from the links what the aim of this is - what is it meant to accomplish? How will success be measured?
Using a medium such as a billboard to get a message to members of a very small niche audience seems like a rather unfocused effort IMO. How many individual JWs will drive along that route and see that one billboard? News about the WTS and JWs has regularly been on TV (reaching far more people) but don't hold your breath waiting for any mass exodus - it just isn't going to happen.
There seems to be a lot of hyperbole going on - claiming that "Millions of people's lives are being adversely affected every day by Jehovah's Witnesses" is a bit of a stretch given that there are only 7 or 8 million JWs in total worldwide. Are 25% of JWs being adversely affected every day?
I understand the desire to "do something" but IMO it's better to make information available for people who are looking for it so that when people are ready to leave they can find the support they need. Trying to make people leave seems like a tall order and trying to fight the WTS on their terms almost madness - they can out-message any amount of ad-spending.
I wish whoever is doing this success though.
As for the sign itself - if the intention is to get the message out about Jehovahs Witnesses then it should say "Jehovahs Witnesses" somewhere on the sign. Using phrases such as Kingdom Hall and Elders will likely mean nothing to non-JWs. If the intention is to reach people with a message then you should be looking to raise conversation with people who may work with JW's for instance.
Something clearer, more direct and more applicable to all readers: