If you’re not familiar with the speed limits in a certain area (and if there are no visible signs anywhere), you’d want to constantly monitor how fast (or slow) you’re going, while at the same time navigating your way in an unfamiliar area. An app called Velociraptor (not related at all to any of the Jurassic Park guys) can help you with that as it is a floating speed monitor that can automatically display on any app that you’re using.
Whether you’re using Google Maps or Waze or HERE, the app can display its floating widget which shows you how fast you’re currently going and what is the speed limit in the area you’re in. You can choose the US or traditional speed signs, the difference being traditional just shows the number in a circle while the US sign has the word Speed Limit over the number. You can also create an alert that will warn you if you are going over the limit (5, 10, 15, or 20% above).
There are also other apps that can do this, but Velociraptor uses Material Design so it looks better. It is also open source so other developers can add some more improvements. And if there are any wrong or missing information, you can go to the OpenStreetMap website and edit the data (well, if you know how).
You can download Velociraptor from the Google Play Store for free. It is also ad-free so that’s one advantage over similar apps and services.