While I model in OO the principal should be similar, I use either neat PVA or UHU for figurers. I remove the base by carefully trimming with a kraft knife then depending on where the figure is to stand I either drill a fine hole in the foot and up into the leg and insert a sewing pin held with UHU or PVA leaving about 5 or so mm projecting from the foot and then drill a matching hole where the figure is to be "Planted". Adding more PVA or UHU to the feet and the pin and then its pushed into the hole.
For free standing I use UHU or Superglue, but I always remove any base as IMO they look far more realistic without the large base.
Signs, steer clear of super glue as this can cause misting of some materials, especially Perspex. Tacywax is one method. Example
https://deluxematerials.co.uk/products/tacky-wax or use neat PVA.