Broadway Stage Grid or Clock or Something like that...

They were probably referring to spikes, or specific spots on the stage normally marked by a special tape. These spikes are sometimes numbered to help actors remember where to stand or where to move to.

In my experience, spike tape is usually used to make sure scenery and props are placed in specific spots, not so much actors.

What you're referring to is probably the number system. Many musicals use a series of (usually even) numbers placed on the ground at the very lip of the stage, so that actors can place themselves with a glance, and easily mirror someone who is supposed to be opposite them in a symmetrical formation. "0" is usually dead center on the stage and then even numbers are evenly spaced out in either direction to the ends of the stage. If you're placed on "6" on SL (stage left), it's an easy way to remember. If you're placed on "5" SL, you simply stand in the empty place between 4 and 6. Next time you sit in a box or front mezzanine, try to spot the numbers at the end of the stage.

EDIT: A1st got there just before me!

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Updated On: 2/26/15 at 08:25 PM

Yes, the numbers system! I've used it for years; it's great when you're in a rehearsal space that may be smaller than your stage because then you don't have to re-space things. I know when "A Funny Thing That Happened on the Way to Forum" ran in 1998, the numbers were Roman numerals, and some of the chorus dancers didn't know which numbers were which.

The picture is fine, just look at his feet, on the red stage... He's standing on 3.

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It's not a grid or a clock. It's just numbers on the front of the stage.