The save ID is the set of numbers at the end of the save link. Your City 4.0 saveID is '213583', for example. I forget how to do linkable signs exactly. I hardly use signs at all, personally, but the instructions are on the forums or someone might read this post and give us that information.
EDIT: Oh yeah, '{c:saveID|Click Text}' Like '{c:213583|See City 4.0 here!}' Put that in the sign, minus the single quotes, of course.
When you click on your save in the browser, either from your profile or the link above, it will bring up the page for it. Look in the address bar for the page it brings up to get the link.