Shivas,
Sorry--we seem to be going back and forth between the rules and the spirit of the rules. I think you have made a very good explanation in that last post, there.
I agree that the line on the putter assists the player in alignment to the line he has chosen. So for you that would have to be against the spirit of the rules, but not the rules.
But if a player goes behind the line, aligns the putter, and then steps into address (like Betsy King always did), then you'd say a line on the putter also indicates a line for putting, which should be against the rules. When aligning the putter astride the ball, there would be no indicating the line and therefore no rule breach.
OK--I can understand that. I don't agree with you about the cheater line being against the rules (or even the spirit of the rules), but I think understand your argument well enough.
And we'll just agree to disagree whether enforcing a ban on cheater lines (or any other mark that could be used to indicate a line for putting) would be practical. I just don't think any benefits of regulating marks on golf balls justifies adding another 20-30 occasions per player per round where actions need to be monitored.
But I'll keep an open mind on it and of course, if the USGA agrees that (a) a rule change is needed, and (b) it is practical to enforce, then I will happily abide by it.
BTW, we have never been in disagreement that the cheater line or trademark indicates a line for putting when aligned to aim down the putting line. Decision 20-3a/2 states the intention as such.
But looking strictly at the language, the USGA obviously does not equate a "trademark aimed along the line of the putt" with a "mark placed". And apparently they don't equate a cheater line with a "mark placed". The question is whether they don't consider the trademark (or cheater line) a "mark", whether they don't consider it "placed", or both.
I might ask the USGA about that and see if I can get an answer (if for no other reason, so I never have to discuss this again!).