I mean - I know this is the accepted wisdom, but I so rarely find it actually works this way.
A cautioned player will either happily accept the caution or they won't. A player who accepts it doesn't need the slow-down, and particularly if it's for some form of cynical SPA (which are most commonly when a player accepts it with a smile), you're only going to wind the other team up taking ages over a caution. And a player who isn't happy to accept the caution will only get more wound up at being asked to spell his name, being made to stand there while you explain the caution, then when he starts to walk away and you have to whistle him back...
Write-on cards where you only need to note a shirt number let you do it either way in my experience. You can flash the card quickly and then note the details after, or you can pull the card out, be clear that it is a caution but still chat to the player for a moment or two as you write the details down before showing the card if you want to. Taking names means you have to do it the slow way, which isn't always the best way.
That's fine unless you are going for promotion or are already between L4 and L2B. Flashing cards will not end well with observers unless there is a very valid reason to do so, such as to defuse a potential serious flashpoint.