When I was single and on my own, I had two close male friends (platonic only) whom I did alot with on a regular basis. One I met in the cafeteria at college (his dorm was next to mine) and the other was in ROTC with me and we also were stationed at the same base. My friend from ROTC attended my wedding and I was so glad he came.
At work, I assumed friendship unless a guy asked me out on weekend dates. If someone from work called to wish me Happy Birthday, I would take that as simple friendship.
If I didn't want to be more than friends, I would insist on paying my own way for everything. Also, if the guy didn't offer to pay, I assumed they just wanted to be friends. Maybe this was a crazy assumption but it mostly seemed to work out.
Once I got married, nothing really changed for me as far as friendships at work go but I no longer have much to do with males unless they are parents of my children's friends, my children's friends or husband's of my girlfriends. I just know my husband wouldn't want me to, so I don't.
I had noticed no one had replied to your question and I hope something here might be helpful?? (Maybe someone younger can correct me if things are different now since I am older? )