You cannot block doorways, egress, etc.The bigger and brighter the sign, and easier to read from the sidewalk, the better.  

Sometimes a simple change to the grade around the foundation can fix the issue or if there is a cement side walk/patio, make sure it’s sealed.

If you do help him, he'll let you believe he's your problem.One concession I did use with my tenants I had to dis-invite (I only ever had to do this with inherited tenants after I learned to screen better) was to tell them that if they left the unit undamaged and really clean and didn't just pile a bunch of stuff out on the sidewalk for me to have to deal with - that I'd give them their deposit back in cash when I received the keys, instead of making them wait 21 days to get it. 

BUT, on the other hand, you will be the one enjoying the new sidewalk.

or from a tenant slipping on a icy sidewalk on your property?

Yes, it is written words, but so is chalk on a sidewalk.

New concrete side walks and stoops in the spring!

The one Sheriff at the door literally grabbed him by his shirt and placed in on the sidewalk outside the front door and he stepped inside. 30 seconds later, saw four adults leave the house - nothing was packed - after 5 months of hell from these people.

This year has been especially bad, they asked me to replace the sidewalks, which I actually did not know the owner was responsible for.

I literally threw my Coinmach machines in the sidewalk.