This is an old thread but maybe someone will notice a new post 
What you are suggesting regarding the hotels and restaurants is a good idea, but the impact of shark fin soup is much broader.
I have lived in China for the past year and a half and every single food store you go into has dozens if not hundreds of dried shark fins. If you figure thousands or tens of thousands of stores, then dozens to hundreds of fins per store, you are conservatively talking over a million fins in Chinese food stores at any one time. Then consider how many are sold and restocked.
For those of you in Europe, if you want to do some good while at home about this issue, boycott Carrefour. Every single Carrefour store I have been to in China has dozens and dozens of shark fins in their dried fish section. This is a European based company, not some Asian food chain who can claim it is their culture. They stock the fins only for financial gain.
If you want to have fun get a picture of shark fins with the giant Carrefour sign in the background. Then publish that back in Europe where people are more sensitive about the issue. Start a boycott Cerrefour website. That will generate some publicity for this entire movement.
Another thing, you are addressing it from the perspective of the person making money off of it (restaurant and hotel owners).
You can't just pick up a picket sign or start signing petitions, you need to consider their culture. If you try to go in and take an aggressive approach like boycotting, to be frank, all you are going to do is piss them off and they will ignore you for patronizing their culture.
I think you would get a much greater impact just educating the general public. China is now much "greener" than you would think. Not only does the average Chinese consume far less paper and plastics then the average westerner, but they are also becoming quite green aware. I am referring educated city residents, not just 'villagers'.
You constantly see pro green commercials on TV here in China. Someone mentioned that as more Chinese gain economical position they too will be able to afford or want to consume shark fin soup, but those same people are much more interested in a "worldly perspective" then just consuming shark fin soup. They tend to have a very willing ear towards conservation.
If it were me and I wanted to make an impact on this issue I would appeal to the National Geographic channel and the Discovery channel to run educational programs on the subject. Most Chinese cable and satellite packages have the channels as an option. (The programs are in Chinese, not English.)
In China every third commercial on Nat Geo or Discovery is a green message because they don't really have a lot or commercials selling products and they need to fill that space each hour. I would guess that for an hour long program, 45 minutes is content, 5 minutes are green messages, 5+ minutes are messages about upcoming programming, and the very small remaining bit is an actual "TV Commercial" as you think of them.
So the Chinese already hear a lot of green messages on a regular basis and it seems well accepted. Nat Geo and Discovery are obviously already leaning the green direction, but due to the absence of me ever seeing any information on shark finning, perhaps they are avoiding broadcasting information because they are afraid of a "cultural conflict".
If you are going to petition anyone, petition Nat Geo and Discovery, who already have the Chinese' eyes and ears every hour of every day. They must have a reason for pushing everything else green but anti shark fin soup messages, plus as eco active groups themselves they should be willing to listen. Maybe if you petition them they will tell you why they have not broadcast much about it, at least not in the past year ad a half that I have been watching.
I saw quite a few programs that you would consider "anti establishment". For example, programs on Tiananmen Square, China's pollution problems, etc. So I can't imagine that Nat Geo and Discovery are being forbidden by China to run a shark fin program, but maybe so...
