I think the signs are a good idea, both to encourage cyclist to ride centerish and with a big yellow diamond bicycle icon to help contribute to motorists awareness of possible cyclists.

Riding far right in a narrow lane with large trucks passing closely is very dangerous as most of us know. I had this happen to me about three years ago and it was a defining moment for me to never ride far right in a narrow lane again. It was a flatbed semi-truck that while it passed I did everything possible to not get bumped by it and pulled under wheels. As soon as it passed I had to pull over in next side street stop and collect my wits for a few minutes before continuing.

Al