Open up a gif on imageready. If you want to post this on tumblr as well, make sure that the size of the gif is 500kb or lower.
Next, add text by using the text tool.
To make it blink, alternate text from the slides by making the layer show, depending on which slide you are on.
Save the image as a gif and there you have it!
*Note: the gif that I used is not mine and all the credits go to the gif maker. I do not know how to make gifs, this tutorial only helps the people who want to add text on it. I do not know how to do this on CS3, CS4 and CS5.
for more tutorials, check the tutorials page on the site.