On most Samsung phones, four ascending bars in the top right corner of the screen indicate the signal strength. A circle with a line through it in the same location indicates that there is no signal. A battery with a lightning bolt inside means that the device is charging.
There are a number of different icons that may appear in the upper right corner of the screen on a Samsung phone. Some indicate the type of mobile data connection the phone is currently accessing. Most of these icons consist of a letter floating above an up and a down arrow. For example, a "G" indicates that the phone is connected to a General Packet Radio Service. GPRS is the slowest type of mobile data connection available, as of 2015. The phone is typically unable to download files on this connection. A "3G," an "H" or a "4G" indicate 3G, HSPA and 4G data connections, respectively. These are all much faster than GPRS.
If the signal strength indicator is displayed with an "R" above it, the phone is roaming and rates may be more expensive. An envelope icon indicates a new text message. An envelope with an "@" symbol on it indicates a new email.