You can type: 

ls -F
This appends a slash (/) to each subdirectory name, and an asterisk (*) to the name of each executable file.  If you want the -F flag in effect every time you give an ls command, make an alias for ls, like this: 
alias ls='ls -F'
Be sure to include the quotation marks.  You can also put this alias command in your .bashrc file so the alias goes into effect automatically every time you log in.