Within reason, it can be a sign of love. Because few people would want to share their significant other with someone else.
HOWEVER, when possessiveness is taken into an extreme (calling every 5 mins to check up on person, getting mad at them for talking platonically to someone of opposite sex, doubting their every move/words/intentions)…THEN...it becomes a sign of insecurity and control issues…an indication of low self-esteem.
^That’s when the “possessiveness” becomes irritating not only for guys but also for girls. ** Both** **genders **want a partner that is confident and secure enough with themselves to show trust and flexibility.