Mode identification

RTTY

Looks like: two narrow lines a fixed shift apart
Width / tones: shifts 85, 170 (amateur default at 45.45 Bd), 200, 450, 850 Hz; each line about 45 Hz
fldigi modem: RTTY
Cursor goes: midpoint of the two lines

sigidwiki → RTTY

CW

Looks like: one line keyed on and off
Width / tones: 1 to 12 Hz
fldigi modem: CW
Cursor goes: the line

CW waterfall: a single dashed line of on-off keying

sigidwiki → Morse Code (CW)

BPSK31 · BPSK63 · BPSK125

Looks like: one steady line, wider with speed
Width / tones: BPSK31: 20 to 45 Hz · BPSK63: 50 to 80 Hz · BPSK125: 100 to 150 Hz
fldigi modem: BPSK31 BPSK63 BPSK125
Cursor goes: line center

BPSK31 waterfall: one narrow continuous line

sigidwiki → PSK

Olivia

Looks like: a grid of hopping dots
Width / tones: 2 to 64 tones in 125 to 2000 Hz; spacing = bandwidth / tones; 8/250 is the usual calling submode
fldigi modem: OLIVIA-8/250 etc.
Cursor goes: center of the block

sigidwiki → Olivia

Contestia

Looks like: the same grid as Olivia
Width / tones: same as Olivia, at twice the symbol rate
fldigi modem: CONTESTIA
Cursor goes: center; only RSID or symbol rate separates it from Olivia

sigidwiki → Contestia

MFSK16 · MFSK8

Looks like: hopping dots
Width / tones: MFSK16: 16 tones at 15.625 Hz, about 316 Hz wide · MFSK8: 32 tones at 7.8 Hz, same width at half the speed
fldigi modem: MFSK16 MFSK8
Cursor goes: center of the block

sigidwiki → MFSK

DominoEX

Looks like: hopping dots
Width / tones: 18 tones; DominoEX 4/5/8/11/16/22 are 173/224/346/262/355/524 Hz wide
fldigi modem: DOMEX11 etc.
Cursor goes: center

sigidwiki → DominoEX

THOR

Looks like: the same grid as DominoEX
Width / tones: same six widths, with forward error correction
fldigi modem: THOR11 etc.
Cursor goes: center; RSID decides

sigidwiki → THOR

THROB

Looks like: slow hopping dots
Width / tones: 9 tones at 8 or 16 Hz, 72 or 144 Hz wide
fldigi modem: THROB
Cursor goes: center

sigidwiki → THROB

MT63

Looks like: a flat continuous block
Width / tones: 64 carriers in 500, 1000 or 2000 Hz; tolerates 120 Hz mistuning
fldigi modem: MT63-500 etc.
Cursor goes: lower edge plus half the width

sigidwiki → MT63

Telling the look-alikes apart

CW and BPSK31 can both show up as the same 30 Hz line. The keying tells them apart. CW has gaps of 40 ms or more where the carrier is off. PSK never stops. A hopping mode is recognized by its energy sitting at separate tone positions from one 30 ms frame to the next. Those tone positions are the dots you see on the waterfall.

Pairs the spectrum cannot separate

The spectrum alone cannot tell Contestia from Olivia, or THOR from DominoEX. For those two pairs, the station's RSID burst tells you which mode it is.