If you are announcing that you gave to the charity you are giving for the acknowledgment which is the wrong reason.
I have worked with loads of charities, awareness does not come from someone saying 'I donated £20 to insert charity' on Facebook.
It's our main goal to spread awareness and support, and it's entirely separate from 'donations' (It's not our purpose to make money, we volunteer and most companies assist for free - volunteering or providing meeting spaces etc... is far more helpful).
If you want to help then share links to research, outreach, events rather than patting your own back which doesn't help.
It's like people who embarrass poor/vulnerable people by filming them at their lowest point while they do a basic human act for them (like giving them a £1 sandwich) just so they can get youtube view.
It's a modern phenomenon and really says a lot about the sad state of humanity.
Also, some people claim they do it 'for' the person who didn't receive a card/gift/favor, etc... and that's worse.
Support charities you believe in but don't force your cause on others who may not be the same (many people disagree with certain charities/causes for moral reasons, their view can easily vary from yours even if you love the cause).
Assuming everyone supports CancerResearch or AbortionRights or PETA and so on because you do is like assuming everyone wants to be told how wonderful your religion is while being gifted the scriptures.
It's not 'nice' it's preachy, forceful, and sometimes downright offensive so just do it for yourself and keep it to yourself unless you know they are of the same persuasion.