how to rename multiple files by replacing string in file name? this string contains a "#"

To replace # by somethingelse for filenames in the current directory (not recursive) you can use the GNU rename utility:

rename  's/#/somethingelse/' *

Characters like - must be escaped with a \.

For your case, you would want to use

rename 's/#U00a9/safe/g' *

Note that if you only want to operate on a certain selection of files, e.g., only *.jpg, adjust the final input to match that selection:

rename 's/#U00a9/safe/g' *.jpg

To perform a test before actually changing filenames, use the -n flag:

demo/> ls                               
Lucky-#U00a9NBC-125x125.jpg  
Lucky-#U00a9NBC-150x150.jpg 

demo/> rename -n 's/#U00a9/safe/g' *.jpg
rename(Lucky-#U00a9NBC-125x125.jpg, Lucky-safeNBC-125x125.jpg)
rename(Lucky-#U00a9NBC-150x150.jpg, Lucky-safeNBC-150x150.jpg)

For OS X, GNU rename can be installed using homebrew: brew install rename.

This is not hard, simply make sure to escape the octothorpe (#) in the name by prepending a reverse-slash (\).

find . -type f -name 'Lucky-*' | while read FILE ; do
    newfile="$(echo ${FILE} |sed -e 's/\\#U00a9/safe/')" ;
    mv "${FILE}" "${newfile}" ;
done 

find the list of files and then replace keyword. below is example

find . -name '*jpg' -exec bash -c ' mv $0 ${0/\#U00a9NBC/safeNBC}' {} \;