Since everyone has been talking about logos that have scared them, I thought I might as well add my own. It was the BBC logo from the very early nineties. (I think they changed in 96 or 97) two lines would come from either side and meet in the middle before the letters BBC would appear, but that bit didn't scared me, it was the ominous music that played in the background.
I loved watching old British comedies as I grew up with them, but I would dread it when someone played a video and that darn logo would come up first. One night I notice my parents watching a British comedy so I sat with them. Then when the tape had finished I made a mercy dash back to my room as the dreaded logo does indeed appear at the end of the tape. I remember one time I told my dad to fast forward that bit as it was scaring me and he just replied: "You're being very silly!" No! I wasn't! It was scaring me!
Then years down the track, I was over at my cousin's place (he was only 3 or 4) and he decided he wanted to watch a cartoon… A BRITISH CARTOON!!! That meant the horrid logo would once again pop up and haunt me. Anyway, the tape was played and I was crouching in my chair when… GASP! THEY CHANGED IT! THEY CHANGED THE BBC LOGO! Instead of the two lines meeting together and playing that horrid music, There were two ribbons floating diagonally with the letter fading in and nice gentle music was playing. I tell you what, I could not tell you how relieved I felt that day. Phew!
There were a few American TV station logos that would scare me with their soundtracks. One was the PBS logo used from 1971 to 1985:
http://www.youtube.com/watch?v=WtGZAoIDe84
There was also the Screen Gems logo: