I think they’re going to have problems, “footlong” hot dogs having been part of the public vernacular for a VERY long time. And I assume a hot dog in bun qualifies as fitting into the category of “sandwich”.
"Footlong" IS a Trademark. It is not a Registered Trademark, but has been used openly by many entities for decades. Subway's trademark registration should not be allowed, and the eatery should get a lawyer and turn on Subway. If they get the right lawyer, they could cause Subway a world of hurt. Subway wants the Trademark, and does not want to buy it from the people using it, so they resort to barratry. Of COURSE Subway is aware of the prior uses.
Serial Number Reg. Number Word Mark Check Status Live/Dead 1 77658312 $5 FOOTLONGS TARR LIVE 2 77752328 FOOTLONG TARR LIVE 3 77324328 FOOTLONG TARR LIVE 4 76586913 2939541 FOOTLONG EXPRESS TARR DEAD 5 75308314 2161133 FOOTLONG EXPRESS TARR DEAD 6 74597430 1948530 WONDERDOGS FRANK FOOTLONG KNOCKWURST TARR DEAD
The first several are not germaine to hot dogs. The last did not specifically claim the use of "footlong".
However, if it already in current use, they have no more right to it than I do for Windows™.
IANAL, I just pay them,