Scale infestations come in 2 forms, hard scale or soft scale. in either case, young insects can travel up several days before setting up a new home. They're strong enough to drop off one plant and find another.  

Hard Scale: Hard scale looks like tiny brown bumps measuring about 1/16th inch in diameter. You can easily spot their shells on the undersides of leaves or lined up along the stem. Once they find a suitable spot, they stick their mouth into a leaf or stem, tuck their legs under and start builds a new protective shell. Scratch with your fingernail or use a knife and it will pop free. Insects live under these shells and feed on your plant while laying eggs for future generations. 

Soft scale resembles a white powdery substance usually found on the underside of leaves or down in the crevices between the leaves.

Like mealy bugs, scale secrete a sticky "honeydew" substance that gives the leaves (and pots) a shiny look. This could be the first sign of trouble that you'll see. "Honeydew" attracts mold and ants.

Controls

Because scale are protected by armored shells, they may be difficult to eradicate. For light infestations:

1. Dislodge the shells with a soft brush and lukewarm soapy water. Make sure you get under the shell.

2. Repeat process whenever insects are seen.