Bobo,
I don't think the idea of Templars (or Sinclair) coming to the Americas a hundred plus years before Columbus or getting silver from Mexico as "nonsense." I know nothing of the production or economics of silver in Europe during the Templar period. However, I've heard "white bearded men from the ocean" was a common theme among Meso-American peoples. Certainly, it is a lot more believable then the discovery of THE holy grail, etc. And, if you're correct about the silver, it introduces interesting questions. Finally, if they were trading with the Americas, it makes sense for them to flee to the other side of the world when the Pope turned on them. Like he would chase them to the western hemisphere?
As far as Templar "treasure signs" go... never heard of any though that doesn't mean they don't exist. There was a rmajor Templar records depository in a castle on some Mediterranean island, but it was destroyed (by the Muslims if I remember correctly). I suppose leads could have been found there... maybe, just maybe (and, they'd probably not be open to it if they existed), the Vatican might have seized Templar documents in their library. I would imaging you'd have to be some sort of Ph.D type to have any hope of viewing them. Most likely, sifting through legend is about the best option (nebulous to be sure).
Relative to Oak Island. I am not sold on it having a Templar connection. The reason? Well, first, I'm not sure if it is actually a cache site. And, second, I remember a core sample that contained (among other things) a piece of parchment with writing on it. To my memory, it was not Latin (rather, English or French). And, it was written in script - it looked nothing like you'd see in the 13th or 14th centuries. I think "leads" may be found in native lore - that may take some digging.
The above being said, Templar treasure is a fascinating thread of history to follow. I think you and others are right, all that wealth didn't just evaporate! There were no banks, unless you include the Tempar system itself and the Pope just nixed it. Historically, there is no doubt they loaded it up on their fleet (the fleet itself another historical fact), and simply sailed away. Unless the ships were lost at sea, it was secreted somewhere. Best of luck to you - the whole thing sounds really cool!