Which truck signs do I need to worry about?

Per your signature you're in a 45 foot RV with a toad. So although truck signs may not apply to you, many of them are there because the road ahead is not wide enough or high enough or of sufficient strength to support a truck. Many truck signs are also designed to keep trucks on designated routes so as to keep the heavy commercial traffic out of residential and business districts. You don't have to worry about those. In California, since you are over 40 feet, you are prohibited from driving on certain roads. However, there are no signs on those roads that tell you that. Instead you are supposed to know when you see the sign that says "No Trucks over 26' Kingpin to Rear Axle" that also means no motorhomes or busses over 40'.