Dental floss or similar worked round the back in a sawing motion might do it. It is often used with things that are stuck on - badges etc. Or just wait, the one stuck with tape on my caravan a few years ago just fell off! Heating with a hair dryer might help to soften the glue.

You could try using a hair dryer or hot water on the front of the plate, if you can locate the sticky bits. That kind of adhesive usually softens at about 70 degC. But try not to deform the plate itself :-)

Last time I removed one I squirted lighter fuel down the back of the plate. It didn't actually dissolve the glue but it did soften it.