I'm going to avoid using real names here, but this situation is real.
There's an open source software called Foo which is used for cooking recipes that's been around for about 13 years and it's released under the AGPL.
A few years ago, another company released their own cooking recipes app under the name FooApp.
There is currently no trademark on Foo. What recourse does Foo have to prevent FooApp from using the word Foo in their branding? Can Foo trademark the name at this point? Can this be used to send FooApp a cease and desist? Is there any recourse under the AGPL?