Is this what it looks like? (lightly slashed tyre)

[Coldrider]

tis nothing but a scratch

[george formby]

I have seen similar with my tyres in the past & had no dramas, funnily enough first time I noticed was on sport demons. My mate had a real puzzler recently, we got back from a ride & checked the tyre's (as you do) & he had a shallow slash right around the front & rear tyres, just off centre. Looked like he had ridden along a stanley knife.

[CookMySock]

That is the point that the manufacturerer joined, spliced, the tread together. It is quite a common sight on worn tyres. I have seen it on reasonably new tyres too, but not often. It seems to be more apparent on cheaper tyres, than the more expensive ones.
I wouldn't worry about it, the tyre looks like it will wear out before the splice gives away.

Yep, and that tyre IS worn out. Wont be long before canvas is showing, and it will just a little slippery in the wet I'd say.

End of life for it.

Steve