Add a symbol to the "Add A Film" dialogue box to control whether the selected film is in your watchlist or not.
From this oft-used pop-up dialogue box, you can already see whether you've rated the selected film and whether you've liked it, and can change those statuses, too. But as it is, you have to open the film's page in a new browser tab before you can see if it's on your watchlist. When searching for various obscure films or browsing related search results in that window, I find myself clicking on films that look interesting from the title/cover, only to find I had already watchlisted them sometime before. This feature would cut down on unnecessary page loading to check/control that status.
Wrong. Once you added a film to watchlist the pop-up box will appear "remove" from watchlist then.
There's also a filter possibility to "hide watchlisted".