ShipStation has a wide array of available hotkey and barcode scan actions. By default, ShipStation indicates when you've triggered one of them. Here's what those indicators look like:
If you ever want to not see them, though, it's super easy to disable.
1. Go to your Account Settings (the wrench icon in the upper right).
2. Select Account and then Display Options from the left-hand sidebar.
3. Find the Hotkey & Barcode Indicator under the General Preferences tab.
4. Set it the way you want, and click Save Changes!
NOTE: Certain actions won't trigger the indicator, regardless of how you set up your account. These include the General Hotkeys, as well as Focus QuickSearch.