assurance
augury
auspice
badge
beacon
bell
caution
clue
divination
flag
flash
foreboding
foreknowledge
foreshadowing
foretoken
forewarning
gesture
giveaway
handwriting on wall
harbinger
herald
high sign
hint
light
manifestation
mark
nod
note
omen
portent
precursor
prediction
premonition
presage
presentiment
prognostic
proof
signal
suggestion
symbol
symptom
token
trace
vestige
warning
wave
whistle
wink
yield
yield sign