Well, the photo is gorgeous, and the restaurant should definitely get credit for correctly pluralizing “dishes”, but that is not how to spell “signature”.
I think the mistake is a phonetic spelling mistake and not a manual typo. The consonant combination “tr” often sounds like “ch” (listen to yourself saying “treasure” or “train”), so I can imagine someone coming up with this by trying to spell what the word sounds like. The “tu” spelling pattern found in words like “nature/natural”, “picture”, and “adventure” is not all that common.
I took this photo outside a restaurant on Mosque Street in Chinatown. I think the restaurant was Chong Qing Grilled Fish. These onions are probably for flavoring the grilled fish.
In one corner of the menu were a bunch of Chinese characters and the English brand “Classical aftertaste”. I think “Classical flavor” was probably more like what they were aiming for. Or “Classic taste”, maybe.