First, please do not use an handmade signature, time will come when you'll have a real one
Then, if it's the same website as the one you are using the Visibility:hidden
tag, we could have a cause for this matter.
This is clearly, with cloaking
, one of the wort thing to attempt. Not because you won't have good results at first, but rather because you take great risks to get blacklisted by the major search engines, which would trash all of your SEO results and efforts so far.
Some medals are easier to win if you cheat, but, you must know such medals can be taken back off any time.
Now talking about how long and before all how to get re indexed in Yahoo!, it's hard to talk about delay, especially with Yahoo!
In all case, first thing to do would be to get rid of all fancy SEO techniques.
Because you still take the risk to get blacklisted by Google as well, and this you don't want.
Then, I know of some blacklisted examples with Google but none with yahoo!. I guess the same advice would apply. Once you've cleaned up your web-site (strictly following the Google advices
is a good start up), write Yahoo! a nice and gentle mail telling you made a mistake and did fix everything in you website, and wait and see.
But this can take time, with Google and if the "mistake" was a real one and got fixed I know of one example where the web site did even get it's PageRank back three weeks after the mail (no answer though).
With yahoo! I don't know, because the web site could as well be reintroduced as totally new. A thing you could try would be to pay for inclusion in the yahoo! directory, it can help out if yahoo! is important for your website. but do it once you have gotten rid of all suspicious coding.