The signature line displays on the test check, but doesn't print on the "Live" check.

One of the reasons this can occur is if you have Vendor Class Security settings in place that override the standard Mekorma Security settings. For example, if on the Mekorma MICR Vendor Class Security window (GP > Tools > Setup > Company > Mekorma MICR Setup > Vendor Class Security) the "When to Print Signatures" field is set to "No Signatures" for the vendor class associated with the vendor, then Signatures will NOT print on live checks but will print on test checks. You should also check the default security settings to see if they are different then what you are expecting. The Test Check uses the default security settings located GP > Tools > Setup > Company > Mekorma MICR Setup> Mekorma MICR Security.