The title is somewhat ambiguous. One gives a rose to a loved one, especially male to female. This suggests that the town loves her, but also that it is somehow a masculine entity to her feminine identity. One also leaves a rose on the grave of someone who is dead. If the town is leaving a rose for her, they are already recognizing she's dead, which, symbolically, she is, long before she dies.
It could also be a trade: a rose for Miss Emily. It also indicates the distance with which she is regarded: this is not Emily, this is Miss Emily. Finally, it refers to the love from Homer that went bad.
A rose is a popular flower symbolizing love, caring, friendship, courtship, peace, respect, etc...
The townspeople admire Emily and respect her as a former aristocrat of society. She is an educator and deserves their care because of all she was forced to endure by her tyrant father. They once seen her as a "monument". "A Rose for Emily" is a dedication to Emily from the townspeople, like an ode is to a great writer.
Well when someone passes away, people ussually send tons of roses. The title says A rose. Meaning 1 rose. So im guessing they did not like her that much?