Most of them have some sort of alignment markings, whether it be a line or a plus sign like on the Newport M putters. However, if you find a putter you like that doesn't have a line on it, you can always send it to the Scotty Cameron Custom Shop and have them put a line on it for you! Good luck.

I think the older models did not have a line. I actually sent mine to the Scotty Cameron Custom shop a few years ago to get it done and it does make a difference to me.

The newer models I believe now have the lines already on them. They look pretty sweet...

There are all kinds of sight lines and dots for putters. Some lines are on the top line, and some are on the flange. There are many ways to see them: one on the top line; one on the flange; one on the flange and on the top line; one on the top line and two or even three on the flange.
They are all as you see 'fit' and are used to give a general line of the ball's path, as you have noted.

This information was taken from Titleist.com under Clubs and the illustration is from the Scotty Cameron Select putters. Hopefully this will answer your question.

Enhanced alignment options including milled flange sight lines and crisscross pop-through visual cues that are matched to head size.