A search of the trademarks shows no one has a trademark for the word Cobra for cars. There are 1004 trademarks listed for 'Cobra' or some variant of Cobra.
Strangely enough, the logo we all know as the Cobra logo was once owned by a security company, not Shelby - this one:
http://www.finishlineaccessories.com/c-42-decals.aspx
Here is a short example of some of the dead trademarks. There are many more dead Cobra trademarks.
Serial Number Reg. Number Word Mark Check Status Live/Dead
1 85860991 SHELBY COBRA DAYTONA COUPE TSDR DEAD
2 85860933 SHELBY COBRA DAYTONA COUPE TSDR DEAD
3 78975170 SHELBY KING COBRA TSDR DEAD
4 78190374 SHELBY KING COBRA TSDR DEAD
5 74617561 CARROLL SHELBY'S COBRA
OIL TSDR DEAD
6 74373789 SHELBY COBRA TSDR DEAD
7 74094588 SHELBY KING COBRA TSDR DEAD