The most obvious signs of spyware depend on what kind of phone you are using. For example, if someone has been tracking your location or reading your text messages, this would be a sign that they may have installed some form of software to do so. If you suspect somebody put spyware onto your device and want to remove it from there but dont know how, try rebooting the device first then removing the malware with an antivirus app such as Malwarebytes for Android