Look for one sharp alone. It will be on the second line from the top of the bass clef. This is an F#, since this line is the F line. An F# indicates the key of G major.
Look for two sharp symbols. They will be located on the second line from the top and third space from the top. These sharps are F# and C#, and they indicate the key of D major.
Look for a collection of three sharps. Besides the previous F# and C#, the third sharp will be a G# and will be located in the top space. This indicates a key of A major.
Look for four sharps. The fourth sharp will be a D# and will be located on the middle line. This indicates a key of E major.
Look for a fifth sharp on the bottom space. This is an A#, and it indicates the key of B major.
Look for a sixth sharp. It will be on the second space from the top. This is an E#, and it indicates the key of F# major.
Look for a seventh sharp on the fourth line from the top. This is a B#, and it indicates the key of C# major.