I agree, some tricks can give this away, best left alone are those ones.
One of the tricks I love to perform is "coin in't bottle."
I use 2 coins, but you can opt for one. With two coins it's more visual.
First I will ask for a 1p coin, then I will remove the lid from bot and ask spectaties to examine the bot and lid. Whilst they do this I will check that coin is magnetic cos all aren't, if not I will use the one I have ready.
Then I will have them sign the coin and put it in't bot and screw lid on.
I will ask if the coin can pass from the bot with lid still on, "NO!" they shout.
Then I will remove lid, pass it to a spec and pretend to tip coin out, but it will stick to ring hid behind my hand, sometimes it don't stick, so I just put it back in and say "it is the same coin you signed, or something like that.
When it stick, hidden by my hand, I ask the spec to screw me, I mean to screw the lid back on.
I hold the bot at an angle they will find impossible to see the coin.
At this stage I am ready to go as I already have the other coin in't my hand.
I hold the coin so as to only show the edge, that way they won't see that it ain't the signed coin, then I slam the coin on't bot, pulling my other hand slightly away from bot, this makes the coin fall to the bottom of bot.
As I shake the bot the other coin slips in't pocket.
Practice this and it will be a winner.
It really does get a great reaction, especially when you give the spec the bot, ask them to remove the coin and examine their signed coin.