Typically after the license key is installed successfully in the software, e.g. a 10-return license key, you should see a green bar with a text like "M/U(10/0)" displayed at the bottom of the software window. It means you can prepare a maximum of 10 returns (denoted by M) and zero return has been used (denoted by U). So M/U means Max/Used.
The following picture shows a license for a maximum of 2000 returns and 126 returns have been used so far in myTaxExpress.
On the other side, if the license is unlicensed, a red bar with the text 'Unlicensed' is displayed.