Connecting to open network Wi-Fi will now be a whole lot more convenient as Android 8.1 Oreo now enables you to see speed of networks before connecting to them.
Public Wi-Fi can be spotty. For the first time, #AndroidOreo 8.1 lets you take out the guesswork & see the speed of networks before you hit connect. Rolling out now: https://t.co/lSzvCFgNk7 pic.twitter.com/60EmoPxUX4
— Android (@Android) January 22, 2018
Network speed will appear in four indicators as Slow, OK, Fast, and Very Fast. Slow can be used for Wi-Fi calling or texts, and OK means that you can read webpages. Fast is for streaming most videos while Very Fast lets you stream high-quality videos.
This new feature is now rolling out to 8.1 devices.
Source: Android

Is it different with the signal indicator on wifi icon?
Yup