I think everyone should back off the guy, he's clearly only just joined the community so he wasn't around when everyone was discussing the hints.
To answer your original question, there were a lot of hints leading to HG/SS such as:
- The news report of the red Gyarados
- Jasmine's appearance in Sunyshore City
- An explicit mention of Professor Elm and his report about eggs
- Cynthia's SecretPotion (which mentions Cianwood City in its bag description, as it did in Generation II)
- The man in the Hotel Grand Lake who mentions Ho-Oh's roost of the Tin Tower and Lugia's home of the Whirl Islands and the fact that Clefairy dance on Monday night in Mt. Moon
- While a Pokémon caught in Sinnoh will display the area it was caught in, and Pokémon sent from Generation III via Pal Park display "Hoenn" or "Kanto", depending on the game in which they were originally caught, the data also includes "Johto", at the time inaccessible through any means.
