I understand that you do not see a wireless symbol in the control center of your Apple Watch Series 3 (GPS + Cellular). I'm happy to provide some help for this.
Check out the information about this in the article below. It still shows the signal strength, but may look different than you expect:
About Bluetooth, Wi-Fi, and cellular on your Apple Watch - Apple Support
Use a cellular network
With Apple Watch Series 3 (GPS + Cellular) and a cellular connection, you can make calls and use data or apps when you don’t have your iPhone or Wi-Fi. Learn how to add your Apple Watch to your cellular plan.
To check your signal strength, swipe up to open Control Center.
The Cellular button turns green when you have a connection. The green dots show the signal strength.
The Cellular button turns white when your cellular plan is active, but your Apple Watch is connected to your iPhone or Wi-Fi.
To turn cellular on or off, swipe up to open Control Center, tap , then turn off Cellular.
Some apps might not update without a connection to your iPhone.
Thanks for using the Apple Support Communities. Cheers!