They are normally marked + and - inside the terminal. You can hook it up either way but it will reverse the flow and you may see a decrease in performance . Here's how we used to check the polarity using a voltmeter years ago.
Hook up a voltmeter with the neg lead to the plug terminal and the pos lead to a ground. Set the meter on the highest volt range. Crank the engine over (don't start it), and you should see an upward reading of the voltmeter(don't worry about the number). If the voltage goes down negative, your coil is hooked up wrong. To correct it reverse coil primary leads. Do not worry about the coil markings, but make note of them for future reference. It will also work with an old school voltmeter. The needle should swing UP and not down.