If you are counting what you are supposed to be counting ... men on the line ... then 10 doesn't matter. I know it's often taught to signal whether your receiver is on or off, but think about it --- does it matter? What really matters? And I know that some like to count who's off instead of who's on - but is that really right? (And in the mechanics with R, U, and L only - this DOES make the most sense and is the exception to what I say below).
Yes, it's hard to count the entire line, but in most mechanics, there are 2 of you to do it. Count your side of the center, and use whatever mechanics you've prediscussed with your partner to signal that number to him.
I have 3, he has 3, we're good. I have 4, he has 2, great. 2 and 4, fantastic. 1 and 5? Uh... what was my signal for five again?!?!?! (

)
But, I have 3, he has two, and BOTH of us flag simulataneously - a thing of beauty and a sign that your crew is working well together.