You could always go to the cop-shop, with your little printed out map you have and explain your case. Ask the on-duty about it, they will at least give you some information for free, then consider going to the lawyer. It may also be worth asking if they get many 'speeders' in your situation, if they do it suggests poor sign positions.
In theory, yes you are guilty as you were going above the limit. If there is no physical way for you to see the signs then you cannot know. Now ... go back sometime and look at that sign, if it says 'begins' you might be screwed. If it does not say 'begins' then it is just a sign. Take pictures of your route showing how you were not in any position to see the other sign.
I have been in a similar situation myself, twice infact. Once I turned from an 80km/h road onto another which was a 60km/h. There was no post for the 60km/h so I continued my usual speed. I got off, but only after I made the cop walk up the road with me to show him. The second time was when an overhanging tree was obscuring the sign and made it invisible. I got off on that one too. I've known enough people get by on it, and also a number who got stung with it. It depends on how you talk to, and how you talk to them.
Interestingly enough my step-daughter got a ticket for 90km/h in a 60km/h zone when it was actually an 80km/h ... she tried to fight it but lost! My sister-in-laws boyfriend also recently got a ticket when a car passing him was tagged, but the cop pulled him over instead! He never fought it, but the cop was not interested in the real speeder either.
