The Window Note

A folded paper note was found taped inside the glass of the rare-plants greenhouse, facing out toward the corridor. The note is hand-written in block capitals and clearly encoded. The lab director wants to know what it says and who left it.

The rules

1. Four people in this building are known to write coded notes. Each has a different cipher style.
2. Six clues describe their habits and one important property of the note itself.
3. Use the clues to decode the message and name the encoder.
4. One submission. You can’t change your answer.