Conditional Data Labels in Charts

I'm trying to automate a bar chart to take the top 5 contributors out of a pool of 50. Its dynamic and will change between time labels.

My issue is that sometimes the data contains 0 values that aren't true zeros. Ie. They represent data that was suppressed. In the chart, I want to make mention of them by having a data label for just those points with an "x" to represent the suppression. 

Ie. I would like a way to have the x data l