Is it advisable to self-advertise in conferences being on the job market
It is ok, but it may not be ideal.  Academia often frowns upon open self-promotion (more than it probably should, in my opinion), and flat out saying that you're on the market in a public presentation seems a little...well, "desperate" is too strong, but the next thing, perhaps. 

Some thoughts about how/when/whether to do this:


Cultural nuances can vary in very subtle and localized ways.  If you are going to a big conference in your profession or field, there must be other people there who are on the job market.  Look to them and see how they are behaving: is anyone else advertising their availability in their presentations?  If not, maybe don't do it yourself without an especially good reason.  If so, look to the audience members and see how they're reacting.  A little face-reading will probably tell you whether people are happy to hear this kind of information.
Consider trying to disburse this information slightly less directly.  For instance, ending a talk with something like "Please come talk to me if you're interested in X [or, by implication, me].  I would be very interested to take these things further."  Then, when someone talks to you one-on-one or in a small group, you can work the fact that you're on the market organically into the conversation.
Whenever you go to a conference and you're on the job market, concentrate on making meaningful academic and social connections with people, especially potential employers.  Don't prioritize selling yourself directly.  If they meet you and like you and your work, you can follow up later by letting them know you're on the market.  And you should.