I was part of a turn around team once that was brought in on a company that was in a similar industry. As we were trying to get a lay of the land we found ourselves in a warehouse -- full of unused promotional items. All purchased at one time or another with logos, branding, and slogans. All intended to be part of a marketing campaign of this kind or another. Some happened, others didn't. Some had the right amount of inventory -- other don't.
Obvioulsy you understand that it is far better to plan a marketing campaign first and then purchase the promotion items which will support that campaign second. The question now is how to use a promotional idea that you have on hand . .. .
Go back to square one: Design a marketing campaign and weave the stickers into it rather than try to find ways to get rid of the stickers.
Who is the target market? Who does the slogan speak to? Job-seekers or job-posters? Who are the stickers for? Where do those people congregate? Why are they congregating there? Are they in a space to think of you? How will the sticker end up on an item that invites and engages them to visit the site?
Perhaps you will create a flyer with a QR code printed on it -- covered by the sticker -- they pull the sticker off and there is a QR code where they enter their information and are entered in a contest for an iPad? Or an invitation to a workshop. . .
Perhaps you will use them as the seal on an envelope or brochure sent to the hiring managers at local companies to give some color to the letter and intrigue them to open it. . . .
Perhaps you will get a worry stone (for people trying to find a job) and put the stickers on them so as they rub it they think of coming to your site. . .
Perhaps you will simply put them on all the bathrooms before a job fair . . . . .
What ever you choose-- there should be a reason: Because it connect your target market to doing something specific that supports your pipeline development.
Your product is a web application used for recruitment? If your targeting a particular population, say programmers for example, you can go to a nearby university CS department and give stickers and brochures detailing your new product to students at a career fair or just putting them on the department bulletin board. Stickers could be used as a supplement to other in hand promotional materials.
The one thing I would add to Joseph's bit is that promo materials like these are becoming less and less worth their cost. I'm afraid to ask how much you spent on the stickers. 5,000 is a lot.
These days you really need to blend your traditional media into social media. Maybe your sticker could say, "Who get's paid more? A pilot or a car mechanic? Post your answer at facebook.com/xcompany"
Then, when they come to your FB page and comment their answer, you interact with them. You ask them why they think that, what their profession is. You open up doors and build relationships.
People aren't going to care about your site if you pass out stickers. When you hand me a sticker I toss it in the garbage. But if I see the sticker in a relevant space, as Joseph said, and it is intriguing and invites engagement, I might pull out my phone and go to your FB page or follow you on twitter. Then, what you do from there will either keep me or turn me off.
Give a shit about your users and prospective users. Invite interaction. Solve their problems in any way you can and every way you can. Blend cool stickers into that, then you win.
There are already ideas here for using the stickers, but the best value you can get out of this purchase of stickers is to learn from your mistake and not repeat it. This will be far more beneficial than whatever you do with the stickers, and count yourself lucky you made this mistake on stickers and not something bigger.
It is important that you don't copy what other companies do without understanding the reasons or making sure it is appropriate for you and your business. If there was one set of steps to follow to make your company a success, everyone would follow those steps and all be doing great, obviously that's not the case.