When Yosh Kawano was the clubhouse manager for the Cubs, he had a unique way to mark the players batting helmets. The players number was painted in white inside the circle of the red C on the front.
You can see Bill Madlock's 18 painted on his helmet.
And here is Don Kessinger's 11
One more, from SSPC's 1976 set with Pete LaCock's #23
But look at this card from SSPC's 1978 set of Joe Wallis. Wallis was #28, but it looks like someone is playing a joke here.
Here is a better look at the helmet. Joe is good 'ol number ? That's a pretty good joke!