I believe someone else may have already pointed this out but both glamdring and orcrist were incredibly feared blades in there time and we're supposed to have slain thousands of goblins this would most likely lead to a rather memorable description amongst the goblins. Another possible reason is that as supported in the link http://tolkien.cro.net/orcs/goblins.html Orcs and goblins are the same thing and as many fans of Tolkiens work know Orcs actually were made from elves that were tortured until they were horribly disfigured and essentialy went insane and also as we may know Elves cannot die of old age so considering this information it is possible that these Goblins/Orcs had seen glamdring and orcrist before.

I believe someone else may have already pointed this out but both Glamdring and Orcrist were incredibly feared blades in their time and were supposed to have slain thousands of goblins. This would most likely lead to a rather memorable description amongst the goblins. Another possible reason is that as supported in the here orcs and goblins are the same thing, and as many fans of Tolkien's work know, Orcs actually were made from elves that were tortured until they were horribly disfigured and essentially went insane. And also as we may know Elves cannot die of old age. So considering this information it is possible that these Goblins/Orcs had seen Glamdring and Orcrist before.