Technician implies more of a "hey, just do your best, whatever. It should work fine, but if you can open the PLC program and determine that a DI isn't coming on you could save us a bit of downtime."
Engineer implies "look, we want you to use your knowledge of how things work to make things work. Make them work well."
Personally I search for SCADA and go through all the ads, then I search for PLC Engineer and go through all of the ads. Engineer helps avoid most of those "Lawyer needed for John Smith PLC" ads. I usually gloss over anything with technician in the title. Also generic ones that don't mention an engineering discipline usually end up being for civil engineering.
Also, for great candidates, advertise what sort of process it is. If I am happy enough at my current job, but haven't figured out how to unsubscribe from job adverts in my inbox, if I see "PLC Engineer" I'm not going to bother filling out an application. But if I see "PLC Engineer at 50MW Glass Plant", I might get excited enough to shoot over a CV and cover letter. This even works if you have what some would consider a terrible process like "PLC Engineer at slaughterhouse".
+1 to including a salary. There is a huge difference between what a good PLC Engineer and a mediocre PLC engineer earn, and also a huge difference between what a PLC Engineer in a 'nice' industry and a PLC in a 'nasty' industry earns.